Magnetoresistive element and magnetic memory device

ABSTRACT

A magnetoresistive element has a ferromagnetic double tunnel junction having a stacked structure of a first antiferromagnetic layer/a first ferromagnetic layer/a first dielectric layer/a second ferromagnetic layer/a second dielectric layer/a third ferromagnetic layer/a second antiferromagnetic layer. The second ferromagnetic layer that is a free layer consists of a Co-based alloy or a three-layered film of a Co-based alloy/a Ni—Fe alloy/a Co-based alloy. A tunnel current is flowed between the first ferromagnetic layer and the third ferromagnetic layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Applications No. 11-262327, filed Sep. 16,1999; No. 11-263741, filed Sep. 17, 1999; No. 2000-265663, filed Sep. 1,2000; and No. 2000-265664, filed Sep. 1, 2000, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a magnetoresistive element havingferromagnetic double tunnel junction, and, a magnetic memory deviceusing the same.

The magnetoresistance effect is a phenomenon that electrical resistancechanges when a magnetic field is applied to a ferromagnetic material. Asthe magnetoresistive element (MR element) using the above effect hassuperior temperature stability within a wide temperature range, it hasbeen used for a magnetic head and a magnetic sensor, and the like.Recently, a magnetic memory device (a magnetoresistive memory or amagnetic random access memory (MRAM)) has also been fabricated. Themagnetoresistive element has been required to have high sensitivity toexternal magnetic field and quick response.

In recent years, there has been found a magnetoresistive element havinga sandwich film in which a dielectric layer is inserted between twoferromagnetic layers, and uses tunnel currents flowing perpendicularlyto the film, so-called a ferromagnetic tunnel junction element (tunneljunction magnetoresistive element, TMR). The ferromagnetic tunneljunction element shows 20% or more of a change rate in magnetoresistance(J. Appl. Phys. 79, 4724 (1996)). Therefore, there has been an increasedpossibility to apply the TMR to a magnetic head and a magnetoresistivememory. However, there is a problem that the magnetoresistance (MR)change is considerably decreased in the ferromagnetic single tunneljunction element, when a voltage to be applied is increased to obtainrequired output voltage (Phys. Rev. Lett. 74, 3273 (1995)).

There has been proposed a ferromagnetic single tunnel junction elementhaving a structure in which an antiferromagnetic layer is provided incontact with one ferromagnetic layer for the ferromagnetic single tunneljunction to make the ferromagnetic layer to be a magnetization pinnedlayer (Jpn. Pat. Appln. KOKAI Publication No. 10-4227). However, such anelement also has a similar problem that the MR change is considerablydecreased when an applied voltage is increased to obtain required outputvoltage.

On the other hand, there has been theoretically estimated that amagnetoresistive element having a ferromagnetic double tunnel junctionforming a stacked structure of Fe/Ge/Fe/Ge/Fe has an increased MR changeowing to spin-polarized resonant tunnel effect (Phys. Rev. B56, 5484(1997)). However, the estimation is based on results at a lowtemperature (8K), and therefore the above phenomenon is not necessarilycaused at room temperature. Note that the above element does not use adielectric such as Al₂O₃, SiO₂, and AlN. Moreover, as the ferromagneticdouble tunnel junction element of the above structure has noferromagnetic layer pinned with an antiferromagnetic layer, there is aproblem that the output is gradually decreased owing to rotation of apart of magnetic moments in a magnetization pinned layer by performingwriting several times when it is used for MRAM and the like.

In addition, there has been proposed a ferromagnetic multiple tunneljunction element comprising a dielectric layer in which magneticparticles are dispersed (Phys. Rev. B56 (10), R5747 (1997); Journal ofApplied Magnetics, 23, 4-2, (1999); and Appl. Phys. LeTT. 73 (19),2829(1998)). It has been expected that the element may be applied to amagnetic head or a magnetoresistive memory, as 20% or more of an MRchange has been realized. In particular, the ferromagnetic double tunneljunction element has an advantage that the reduction in the MR changecan be made low even with increased applied voltage. However, as theelement has no ferromagnetic layer pinned with an antiferromagneticlayer, there is a problem that the output is gradually decreased owingto rotation of a part of magnetic moments in a magnetization pinnedlayer by performing writing several times when it is used for MRAM andthe like. As a ferromagnetic double tunnel junction element using aferromagnetic layer consisting of a continuous film (Appl. Phys. Lett.73(19), 2829(1998)) has a ferromagnetic layer consisting of a singlelayer film of, for example, Co, Ni₈₀Fe₂₀ between dielectric layers,there are problems that a reversal magnetic field for reversing themagnetic moment may not be freely designed, and that coercive force ofthe ferromagnetic layer may be increased when the material such as Co isprocessed.

For application of the ferromagnetic tunnel junction element to MRAM andthe like, external magnetic fields are applied to a ferromagnetic layer(free layer, or a magnetic recording layer), magnetization of which isnot pinned, by flowing current in a wire (bit line or word line) inorder to reverse the magnetization of the magnetic recording layer.However, since increased magnetic fields (switching magnetic fields) arerequired for reversing the magnetization of the magnetic recording layeras memory cells become smaller, it is necessary to flow a high currentin the wire for writing. Thus, power consumption is increased forwriting as memory capacity of the MRAM is increased. For example, in anMRAM device with a high density of 1 Gb or more, there may be caused aproblem that the wires melt owing to increased current density forwriting in the wires.

As one solution for the above problem, an attempt is made to carry outmagnetization reversal by injecting spin-polarized current (J. Mag. Mag.Mat., 159 (1996) L1; and J. Mag. Mag. Mat., 202(1999) 157). However, themethod for performing magnetization reversal by injection of the spincurrent causes increase in current density in the TMR element, whichleads to destruction of a tunnel insulator. Moreover, there have been noproposals for an element structure suitable for spin injection.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a magnetoresistiveelement of a tunnel junction type and a magnetic memory device in thatreduction in the MR change can be made low even when an applied voltageis increased to obtain required output voltage, that have no problemthat an output is gradually decreased owing to rotation of a part ofmagnetic moments in the magnetization pinned layer by repeated writing,and in that an reversal magnetic field for reversing the magneticmoments in the ferromagnetic layer can be freely designed.

Another object of the present invention is to provide a magnetoresistiveelement of a tunnel junction type and a magnetic memory device that cansuppress increase in reversal magnetic field for reversing themagnetization of the magnetic recording layer accompanying scaling downof memory cells.

Still another object of the present invention is to provide a magneticmemory device that has a structure suitable for spin injection and cancontrol current density in a wire and a TMR element, and a method forwriting information to the magnetic memory device.

A first magnetoresistive element of the present invention comprises aferromagnetic double tunnel junction having a stacked structure of afirst antiferromagnetic layer/a first ferromagnetic layer/a firstdielectric layer/a second ferromagnetic layer/a second dielectriclayer/a third ferromagnetic layer/a second antiferromagnetic layer; thesecond ferromagnetic layer consists of a Co-based alloy, or athree-layered film of a Co-based alloy/a Ni—Fe alloy/a Co-based alloy;and a tunnel current is flowed between the first ferromagnetic layer andthe third ferromagnetic layer.

A second magnetoresistive element of the present invention comprises aferromagnetic double tunnel junction having a stacked structure of afirst ferromagnetic layer/a first dielectric layer/a secondferromagnetic layer/a first antiferromagnetic layer/a thirdferromagnetic layer/a second dielectric layer/a fourth ferromagneticlayer; the first and fourth ferromagnetic layers consist of a Co-basedalloy or a three-layered film of a Co-based alloy/a Ni—Fe alloy/aCo-based alloy; and a tunnel current is flowed between the firstferromagnetic layer and the fourth ferromagnetic layer.

A third magnetoresistive element of the present invention comprises aferromagnetic double tunnel junction having a stacked structure of afirst antiferromagnetic layer/a first ferromagnetic layer/a firstdielectric layer/a second ferromagnetic layer/a second antiferromagneticlayer/a third ferromagnetic layer/a second dielectric layer/a fourthferromagnetic layer/a third antiferromagnetic layer; the first andfourth ferromagnetic layers or the second and third ferromagnetic layersconsist of a Co-based alloy or a three-layered film of a Co-basedalloy/a Ni—Fe alloy/a Co-based alloy; and a tunnel current being flowedbetween the first ferromagnetic layer and the fourth ferromagneticlayer.

A fourth magnetoresistive element of the present invention comprises aferromagnetic double tunnel junction having a stacked structure of afirst ferromagnetic layer/a first dielectric layer/a secondferromagnetic layer/a first nonmagnetic layer/a third ferromagneticlayer/a second nonmagnetic layer/a fourth ferromagnetic layer/a seconddielectric layer/a fifth ferromagnetic layer; the second, third andfourth ferromagnetic layers adjacent to each other areantiferromagnetically coupled through the nonmagnetic layers; the firstand fifth ferromagnetic layers consist of a Co-based alloy or athree-layered film of a Co-based alloy/a Ni—Fe alloy/a Co-based alloy;and a tunnel current is flowed between the first ferromagnetic layer andthe fifth ferromagnetic layer.

In the magnetoresistive elements of the present invention, the thicknessof the Co-based alloy or the above three-layered film of the Co-basedalloy/the Ni—Fe alloy/the Co-based alloy is preferably 1 to 5 nm.

A magnetic memory device of the present invention comprises a transistoror a diode, and any one of the first to fourth magnetoresistive element.

The magnetic memory device of the present invention comprises atransistor or a diode and the first or third magnetoresistive element,and at least the uppermost antiferromagnetic layer in themagnetoresistive element constitutes a part of a bit line.

Another magnetic memory device of the present invention comprises afirst magnetization pinned layer whose magnetization direction ispinned, a first dielectric layer, a magnetic recording layer whosemagnetization direction is reversible, a second dielectric layer, and asecond magnetization pinned layer whose magnetization direction ispinned; the magnetic recording layer comprises the three-layered film ofa magnetic layer, a nonmagnetic layer and a magnetic layer, two magneticlayers constituting the three-layered film being antiferromagneticallycoupled; and magnetization directions of the magnetization pinned layersin regions in contact with the dielectric layer are substantiallyanti-parallel to each other.

Still another magnetic memory device of the present invention comprises,a first magnetization pinned layer whose magnetization direction ispinned, a first dielectric layer, a magnetic recording layer whosemagnetization direction is reversible, a second dielectric layer, and asecond magnetization pinned layer whose magnetization direction ispinned; the magnetic recording layer comprising a three-layered film ofa magnetic layer, a nonmagnetic layer and a magnetic layer, the twomagnetic layers constituting the three-layered film beingantiferromagnetically coupled; the second magnetization pinned layercomprising a three-layered film of a magnetic layer, a nonmagnetic layerand a magnetic layer, the two magnetic layers constituting thethree-layered film being antiferromagnetically coupled; a length of thefirst magnetization pinned layer being formed longer than those of thesecond magnetization pinned layer and the magnetic recording layer; andmagnetization directions of the two magnetization pinned layers inregions in contact with the dielectric layer being substantiallyanti-parallel to each other.

A method for writing information to the above magnetic memory devicescomprises steps of: supplying the magnetic recording layer with a spincurrent through the first or second magnetization pinned layer; andflowing a current in a wire for writing so as to apply a currentmagnetic field to the magnetic recording layer.

Still another magnetoresistive element of the present inventioncomprises a ferromagnetic double tunnel junction having a stackedstructure of a first antiferromagnetic layer/a first ferromagneticlayer/a first tunnel insulator/a second ferromagnetic layer/a firstnonmagnetic layer/a third ferromagnetic layer/a second nonmagneticlayer/a fourth ferromagnetic layer/a second tunnel insulator/a fifthferromagnetic layer/a second antiferromagnetic layer; the second andthird ferromagnetic layers are antiferromagnetically coupled through thefirst nonmagnetic layer; and the third and fourth ferromagnetic layersare antiferromagnetically coupled through the second nonmagnetic layer.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 shows a sectional view of a basic structure of a firstmagnetoresistive element of the present invention;

FIG. 2 shows a sectional view of a basic structure of a secondmagnetoresistive element of the present invention;

FIG. 3 shows a sectional view of a basic structure of a thirdmagnetoresistive element of the present invention;

FIG. 4 shows a sectional view of a basic structure of a fourthmagnetoresistive element of the present invention;

FIG. 5 shows a sectional view of a basic structure of another embodimentof the fourth magnetoresistive element of the present invention;

FIG. 6 shows an equivalent circuit diagram of an MRAM combining MOStransistors and ferromagnetic double tunnel junction elements;

FIG. 7 shows a sectional view of the MRAM in FIG. 6 in which a pinnedlayer of the ferromagnetic double tunnel junction element constitutes apart of a bit line;

FIG. 8 shows an equivalent circuit diagram of an MRAM combining diodesand ferromagnetic double tunnel junction elements;

FIG. 9 shows a sectional view of the MRAM in FIG. 8 in which a pinnedlayer of the ferromagnetic double tunnel junction element constitutes apart of a bit line;

FIG. 10 shows a sectional view of a ferromagnetic double tunnel junctionelement used for another MRAM of the present invention;

FIG. 11 shows a sectional view of a ferromagnetic double tunnel junctionelement used for still another MRAM of the present invention;

FIG. 12 shows a sectional view of a ferromagnetic double tunnel junctionelement used for still another MRAM of the present invention;

FIG. 13 shows a sectional view of an example of an MRAM according to thepresent invention;

FIG. 14 shows a sectional view of another example of an MRAM accordingto the present invention;

FIG. 15 shows a sectional view of another example of a magnetoresistiveelement according to the present invention;

FIG. 16 shows a sectional view of still another example of amagnetoresistive element according to the present invention;

FIG. 17 shows a sectional view of still another example of amagnetoresistive element according to the present invention;

FIG. 18 shows a perspective view of a magnetic head assembly providedwith a magnetoresistive head comprising a tunnel junctionmagnetoresistive element according to the present invention;

FIG. 19 shows a perspective view of the internal structure of a magneticdisk apparatus provided with the magnetic head assembly shown in FIG.18;

FIG. 20 shows a graph of magnetoresistive curves of the samples A and Bin Embodiment 1;

FIG. 21 shows a graph of applied voltage dependency of MR change for thesamples A, B and C in Embodiment 1;

FIG. 22 shows a graph of relationships between reversal cycles of pulsedmagnetic field and an output voltage for the samples A, B and D inEmbodiment 1;

FIG. 23 shows a graph of magnetoresistive curves of the samples A2 andB2 in Embodiment 2;

FIG. 24 shows a graph of applied voltage dependency of MR change for thesamples A2, B2 and C2 in Embodiment 2;

FIG. 25 shows a graph of relationships between reversal cycles of pulsedmagnetic field and an output voltage for the samples A2, B2 and D2 inEmbodiment 2;

FIG. 26 shows a graph of magnetoresistive curves of the samples A3 andB3 in Embodiment 3;

FIG. 27 shows a graph of applied voltage dependency of MR change for thesamples A3, B3 and C3 in Embodiment 3;

FIG. 28 shows a graph of relationships between reversal cycles of pulsedmagnetic field and an output voltage for the samples A3, B3 and D3 inEmbodiment 3;

FIG. 29 shows a graph of magnetoresistive curves of the samples A4 andB4 in Embodiment 4;

FIG. 30 shows a graph of applied voltage dependency of MR change for thesamples A4, B4 and C4 in Embodiment 4;

FIG. 31 shows a graph of relationships between reversal cycles of pulsedmagnetic field and an output voltage for the samples A4, B4 and D4 inEmbodiment 4;

FIG. 32 shows a sectional view of a magnetoresistive element inEmbodiment 5 in which a pinned layer constitutes a part of a bit line;

FIG. 33 shows a graph of magnetoresistive curves of the samples A5 andB5 in Embodiment 5;

FIG. 34 shows a graph of applied voltage dependency of MR change for thesamples A5, B5 and C5 in Embodiment 5;

FIG. 35 shows a graph of relationships between reversal cycles of pulsedmagnetic field and an output voltage for the samples A5, B5, D5 and E5in Embodiment 5;

FIG. 36 shows a graph of relationships between a junction width and anMR change for the samples T1, T2 and T3 in Embodiment 7; and

FIG. 37 shows a graph of applied voltage dependency of MR change for thesamples T1, T2 and T3 in Embodiment 7.

DETAILED DESCRIPTION OF THE INVENTION

Basic structures of magnetoresistive elements according to the presentinvention will be described hereinafter, referring to FIGS. 1 to 4.

FIG. 1 shows a first magnetoresistive element of the present invention.The magnetoresistive element 10 forms a ferromagnetic double tunneljunction having a stacked structure of a first antiferromagnetic layer11/a first ferromagnetic layer 12/a first dielectric layer 13/a secondferromagnetic layer 14/a second dielectric layer 15/a thirdferromagnetic layer 16/a second antiferromagnetic layer 17. In theelement, a tunnel current is flowed between the first ferromagneticlayer and the third ferromagnetic layer. In the element, the first andthird ferromagnetic layers 12, 16 are a pinned layer (a magnetizationpinned layer), and the second ferromagnetic layer 14 is a free layer (amagnetic recording layer in the case of an MRAM). In the firstmagnetoresistive element, the second ferromagnetic layer 14 that is afree layer consists of a Co-based alloy (for example, Co—Fe, Co—Fe—Ni,and the like) or a three-layered film of a Co-based alloy/a Ni—Fealloy/a Co-based alloy.

FIG. 2 shows a second magnetoresistive element of the present invention.The magnetoresistive element 20 forms a ferromagnetic double tunneljunction having a stacked structure of a first ferromagnetic layer 21/afirst dielectric layer 22/a second ferromagnetic layer 23/anantiferromagnetic layer 24/a third ferromagnetic layer 25/a seconddielectric layer 26/a fourth ferromagnetic layer 27. In the element, atunnel current is flowed between the first ferromagnetic layer and thefourth ferromagnetic layer. In the element, the second and thirdferromagnetic layers 23, 25 are a pinned layer, and the first and fourthferromagnetic layers 21, 27 are a free layer (a magnetic recording layerin the case of an MRAM). In the second magnetoresistive element, thefirst and fourth ferromagnetic layers 21, 27 that are a free layerconsist of a Co-based alloy (for example, Co—Fe, Co—Fe—Ni, and the like)or a three-layered film of a Co-based alloy/a Ni—Fe alloy/a Co-basedalloy.

FIG. 3 shows a third magnetoresistive element of the present invention.The magnetoresistive element 30 forms a ferromagnetic double tunneljunction having a stacked structure of a first antiferromagnetic layer31/a first ferromagnetic layer 32/a first dielectric layer 33/a secondferromagnetic layer 34/a second antiferromagnetic layer 35/a thirdferromagnetic layer 36/a second dielectric layer 37/a fourthferromagnetic layer 38/a third antiferrimanetical layer 39. In theelement, a tunnel current is flowed between the first ferromagneticlayer and the fourth ferromagnetic layer. In the element, when thesecond and third ferromagnetic layers 34, 36 are designed as a pinnedlayer, the first and fourth ferromagnetic layers 32, 38 are made to be afree layer (a magnetic recording layer in the case of an MRAM). On theother hand, when the first and fourth ferromagnetic layers 32, 38 aredesigned as a pinned layer, the second and third ferromagnetic layers34, 36 are made to be a free layer (a magnetic recording layer, in thecase of an MRAM). In the third magnetoresistive element, either a groupof the first and fourth ferromagnetic layers 34, 36, or that of thesecond and third ferromagnetic layers 34, 36, each of which is used as afree layer, consists of a Co-based alloy (for example, Co—Fe, Co—Fe—Ni,and the like) or a three-layered film of a Co-based alloy/a Ni—Fealloy/a Co-based alloy.

FIG. 4 shows a fourth magnetoresistive element of the present invention.The magnetoresistive element 40 forms a ferromagnetic double tunneljunction having a stacked structure of a first ferromagnetic layer 41/afirst dielectric layer 42/a second ferromagnetic layer 43/a firstnonmagnetic layer 44/a third ferromagnetic layer 45/a second nonmagneticlayer 46/a fourth ferromagnetic layer 47/a second dielectric layer 48/afifth ferromagnetic layer 49. In the element, a tunnel current is flowedbetween the first ferromagnetic layer and the fifth ferromagnetic layer.In addition, the second, third and fourth ferromagnetic layers 43, 45,47 adjacent to each other are antiferromagnetically coupled throughnonmagnetic layers 44, 46. In the element, the second to fourthferromagnetic layers 43, 45, 47 are a pinned layer, and the first andfifth ferromagnetic layers 41, 49 are a free layer (a magnetic recordinglayer in the case of an MRAM). In the fourth magnetoresistive element,the first and fifth ferromagnetic layers 41, 49 that are a free layerconsist of a Co-based alloy (for example, Co—Fe, Co—Fe—Ni, and the like)or a three-layered film of a Co-based alloy/a Ni—Fe alloy/a Co-basedalloy.

FIG. 5 shows a variation of the fourth magnetoresistive element. In themagnetoresistive element shown in FIG. 5, a structure in which anantiferromagnetic layer is inserted between the ferromagnetic layers,that is, a three-layered film of a ferromagnetic layer 45 a/anantiferromagnetic layer 50/a ferromagnetic layer 45 b is provided,instead of the third ferromagnetic layer 45 shown in FIG. 4.

Note that, an antiferromagnetic layer may be provided in contact with atleast one of the second and fourth ferromagnetic layers 43, 47constituting the fourth magnetoresistive element.

As the magnetoresistive elements according to the present inventionhaving a ferromagnetic double tunnel junction comprises at least twodielectric layers, an effective voltage applied to one tunnel junctionis low. Therefore, the elements have an advantage that their voltagedependency of MR change is not remarkable, that is, reduction in the MRchange is made low even when an applied voltage is increased in order toobtain a required output voltage.

In the above four basic structures of the magnetoresistive elementhaving a ferromagnetic double tunnel junction according to the presentinvention, spins in the magnetization pinned layer (a pinned layer) arepinned with the antiferromagnetic layer or the antiferromagneticcoupling. Therefore, it may be possible to prevent the problem that theoutput is gradually decreased owing to rotation of the magnetic momentsin the magnetization pinned layer by repeated writing.

In addition, the magnetoresistive elements use a Co-based alloy (Co—Feand Co—Fe—Ni, and the like) or a three-layered film of a Co-basedalloy/a Ni—Fe alloy/a Co-based alloy, whose magnetostriction is low, forthe free layer (magnetic recording layer). The free layers are thesecond ferromagnetic layer 14 in FIG. 1, the first and fourthferromagnetic layers 21 and 27 in FIG. 2, either a group of the firstand fourth ferromagnetic layers 32, 38 or a group of the second andthird ferromagnetic layers 34, 36, and the first and the fifthferromagnetic layer 41, 49 in FIGS. 4 and 5. Therefore, the reversalmagnetic field is controlled to a low value, which enables to lower acurrent flowed in a wire to apply a current magnetic field. When thethree-layered film of a Co-based alloy/a Ni—Fe alloy/a Co-based alloy isused for the free layer, magnitude of the reversal magnetic field may befreely designed by control of the thickness ratio of each layer.

In particular, in the magnetoresistive element having the structureshown in FIG. 3, the reversal magnetic field is determined not by themagnetic coercive force of the magnetic material, but by the exchangemagnetic field caused on the interface between a magneticmaterial/antiferromagnetic material. Advantageously, the exchangemagnetic field may be freely designed by control of the type, thicknessand alloy composition of the first and third antiferromagnetic layers31, 39 and the second antiferromagnetic layer 35. Thus, the basicstructure of FIG. 3 exhibits the most preferable characteristics amongthe above four basic structures. Moreover, the structure of FIG. 3 isespecially effective in the case of where a processing size is loweredto sub-micron and a junction area is made very small. That is, in thecase where a processing size is lowered to sub-micron, the writingmagnetic field tends to be irregular due to process damage or influenceof domains of the free layer (magnetic recording layer). Where anantiferromagnetic layer is provided in contact with the free layer(magnetic recording layer) as the structure shown in FIG. 3, it may bepossible to prevent the irregularity of the writing magnetic field, asthe writing magnetic field may be designed based on the exchangemagnetic field. Therefore, the yield of the element may be remarkablyimproved.

On the other hand, it is preferable to make the whole thickness of theelement thin in order to improve processing accuracy in fine processingof the element of the present invention. In this point, it is preferableto adopt structures as shown in FIGS. 2, 4 and 5 which make it possibleto reduce the number of the antiferromagnetic layers as much aspossible.

Then, materials for use in each layer of a magnetoresistive element ofthe present invention will be described below.

As mentioned above, a Co-based alloy (Co—Fe, CO—Fe—Ni, and the like) ora three-layered layer of a Co-based alloy/Ni—Fe alloy/a Co-based alloyis used for the free layer (magnetic recording layer). Further, a smallamount of nonmagnetic elements such as Ag, Cu, Au, Al, Mg, Si, Bi, Ta,B, C, O, N, Si, Pd, Pt, Zr, Ir, W, Mo, and Nb may be added to the abovealloys. The magnetoresistive element of the present invention may beapplied to a magnetoresistive magnetic head, a magnetic memory device, amagnetic field sensor, and the like. In the above applications, it ispreferable to provide uniaxial anisotropy to the free layer.

The thickness of the free layer may be preferably 0.1 nm to 100 nm, morepreferably 0.5 to 50 nm, and most preferably 1 to 5 nm. When thethickness of the free layer is less than 1 nm, there is a possibilitythat the free layer is not made into a continuous film, but is made intoa so-called granular structure in which ferromagnetic particles aredispersed in a dielectric layer. As a result, it becomes difficult tocontrol the junction characteristics, and there is a possibility thatthe switching magnetic field becomes irregular. Moreover, there may becaused a problem that fine particles are made to be superparamagnetic ata room temperature which leads to extremely reduction in the MR change.On the other hand, when the thickness of the free layer exceeds 5 nm,the reversal magnetic field may exceed 100 Oe which requires to flow ahigh current in a wire in a case where, for example, themagnetoresistive element is applied to an MRAM designed by 0.25 μm rule.In addition, when the thickness of the free layer exceeds 5 nm, the MRchange is reduced with increased bias voltage, that is, the so-calledbias dependency becomes remarkable. If the thickness of the free layeris in a range of 1 to 5 nm, the increase of the reversal magnetic fieldand the bias dependency of the MR change, which may be caused by fineprocessing, can be controlled. Moreover, if the thickness of the freelayer is in the above range, the processing accuracy also becomesexcellent.

Materials used for the pinned layer are not particularly limited, andFe, Co, Ni or their alloys, a magnetite having high spin polarizability,an oxide such as CrO₂ and RXMnO_(3−y) (where R represents an rare earthelement, and X represents Ca, Ba or Sr), a Heusler alloy such as NiMnSband PtMnSb, and the like may be used. The pinned layer is required to beso thick that it does not become superparamagnetic, and may bepreferably 0.4 nm or more. Moreover, as long as the ferromagnetism isnot lost, a small amount of nonmagnetic elements such as Ag, Cu, Au, Al,Mg, Si, Bi, Ta, B, C, O, N, Si, Pd, Pt, Zr, Ir, W, Mo and Nb may beadded to the above magnetic materials.

When the pinned layer is desired to be strongly pinned with theantiferromagnetic layer, a three-layered film of a ferromagnetic layer/anonmagnetic layer/a ferromagnetic layer may be used as a pinned layer sothat the two-layered ferromagnetic layers may be antiferromagneticallycoupled through a nonmagnetic layer. Materials for the nonmagnetic layerare not particularly limited, and a metal such as Ru, Ir, Cr, Cu and Rhmay be used. The antiferromagnetic coupling can be caused between themagnetic layers by adjusting the thickness of the nonmagnetic layer. Thethickness of the nonmagnetic layer may be preferably 0.5 to 2.5 nm.Considering the thermal resistance and the strength of theantiferromagnetic coupling, the thickness of the nonmagnetic layer maybe more preferably 0.7 to 1.5 nm. Specifically, a three-layered filmsuch as Co (or Co—Fe)/Ru/Co (or Co—Fe), and Co (or Co—Fe)/Ir/Co (orCo—Fe) may be used.

As materials for the antiferromagnetic layer, Fe—Mn, Pt—Mn, Pt—Cr—Mn,Ni—Mn, Ir—Mn, NiO, Fe₂O₃ and the like may be used.

As materials for the dielectric layer, Al₂O₃, SiO₂, MgO, AlN, Bi₂O₃,MgF₂, CaF₂, SrTiO₂ AlLaO₃ and the like may be used. The loss of oxygen,nitrogen or fluorine in the dielectric layer may be allowed. Althoughthe thickness of the dielectric layer is not particularly limited, thedielectric layer is preferable made thin, and it may be preferably 10 nmor less, and more preferably 5 nm or less.

A substrate on which a magnetoresistive element of the present inventionis formed is not particularly limited. Various types of substrate suchas Si, SiO₂, Al₂O₃, spinel and AlN may be used. In the presentinvention, the magnetoresistive element may be stacked on the substratewith intervening an underlayer therebetween, and a protective layer maybe provided on the magnetoresistive element. As materials for theunderlayer and protective layer, Ta, Ti, W, Pt, Pd, Au, Ti/Pt, Ta/Pt,Ti/Pd, Ta/Pd or nitride such as TiN_(X) may be preferably used.

A magnetoresistive element according to the present invention may befabricated by depositing each layer with usual deposition methods suchas various types of spattering, vacuum evaporation and molecular beamepitaxy.

Next, a magnetic memory device (MRAM) using a magnetoresistive elementof the present invention will be described below. The MRAM using themagneto-resistive element of the present invention may obtain an effectthat a current flowing in a wire to apply the current magnetic field maybe reduced even in both cases of non-destructive reading and destructivereading.

As a specific constitution, there has been conceived a structure inwhich the ferromagnetic double tunnel junction element is stacked on atransistor, or a structure in which a diode and the ferromagnetic doubletunnel junction are stacked. As described below, it is particularlypreferable to apply the first or third ferromagnetic double tunneljunction element to the structures, and to use at least the uppermostanti-ferromagnetic magnetic layer as a part of a bit line.

An MRAM having a structure in which, for example, a first ferromagneticdouble tunnel junction element (FIG. 1) is stacked on a MOS transistorwill be described below, referring to FIGS. 6 and 7. FIG. 6 shows a viewof an equivalent circuit of an MRAM of 3×3 cells. FIG. 7 shows asectional view of an MRAM in a single cell.

As shown in the equivalent circuit diagram of FIG. 6, memory cells eachcomprising the transistor 60 and the ferromagnetic double tunneljunction element (TMR) 10 of FIG. 1 are arrayed in a matrix. The wordline for reading (WL1) 62 constituted by the gate electrode of thetransistor 60, and the word line for writing (WL2) 71 are parallel toeach other. The bit line (BL) 74 connected to the other end (upper part)of the TMR 10 is arranged in perpendicular to the word line (WL1) 62 andthe word line (WL2) 71.

As shown in FIG. 7, the transistor 60 comprises the silicon substrate61, the gate electrode 62, the source and drain regions 63, 64. The gateelectrode 62 constitutes the word line for reading (WL1). The word linefor writing (WL2) 71 is formed on the gate electrode 62 and aninsulator. The contact metal 72 is connected to the drain region 64 ofthe transistor 60, and the underlayer 73 is connected to the contactmetal 72. The ferromagnetic double tunnel junction element (TMR) 10 ofFIG. 1 is provided on the underlayer 73 at a position above the wordline for writing (WL2) 71. That is, the following layers are stacked onthe underlayer 73: an antiferromagnetic layer 11/a first ferromagneticlayer (pinned layer) 12/a first dielectric layer 13/a secondferromagnetic layer (free layer) 14/a second dielectric layer 15/a thirdferromagnetic layers (pinned layers) 16 a and 16 b/a secondantiferromagnetic layer 17. In this embodiment, the pinned layer isconstituted by the two layers 16 a and 16 b. The metal layer of the bitline (BL) 74 is formed on the second antiferromagnetic layer 17 of theTMR 10.

The area of the second ferromagnetic layer 14 of a free layer isdifferent from that of the upper antiferromagnetic layer 17 and thepinned layer 16 b. The upper antiferromagnetic layer 17 and the pinnedlayer 16 b form a part of the bit line 74. More specifically, the bitline 74 has a stacked structure of a pinned layer 16 b/anantiferromagnetic layer 17/a metalic layer. Note that, the bit line 74may be constituted by the antiferromagnetic layer 17/the metal layer,without providing the pinned layer 16 b having the same area as that ofthe antiferromagnetic layer 17 under the layer 17.

In this structure, spins in the pinned layers 16 b and 16 a are morestably pinned with the antiferromagnetic layer 17 having a large area,and magnetic moments in the pinned layers 16 b and 16 a are not rotatedeven by repeated writing. Thus, reduction in output can be effectivelyprevented.

Further, the structure above the free layer 14 of the TMR 10 is formedby deposition and patterning of the free layer 14/the second dielectriclayer 15/the pinned layer 16 a, and those of the pinned layer 16 b/theantiferromagnetic layer 17/the metal layer. Conventionally, thestructure above the free layer 14 of the TMR 10 has been formed bydeposition and patterning of the free layer 14/the second dielectriclayer 15/the pinned layer 16 a/the antiferromagnetic layer 17, and thoseof the bit line metal layer. Thus, when the structure shown in FIG. 7 isadopted, as the patterning process of the comparatively thickantiferromagnetic layer 17 is separated to another process, it ispossible to make the thickness of the films to be finely processed atone time thin, in the above former patterning. Therefore, it is possibleto reduce process damage to the region of the ferromagnetic tunneljunction, and to improve processing accuracy.

An MRAM having a structure in which a diode and, for example, a firstferromagnetic double tunnel junction element (FIG. 1) will be describedbelow, referring to FIGS. 8 and 9. FIG. 8 shows a view of an equivalentcircuit diagram of an MRAM of 3×3 cells. FIG. 9 shows a perspective viewof the MRAM.

As shown in the equivalent circuit diagram of FIG. 8, memory cells eachhaving a stacked structure of a diode 80 and TMR 10 are arrayed in amatrix. The stacked structure of the diode 80 and TMR 10 is formed onthe word line (WL) 91 such that the word line (WL) 91 is connected toone end of the diode 80. The bit line (BL) 92 arranged in perpendicularto the word line (WL) 91 is connected to the other end of the TMR 10.

As shown in FIG. 9, the silicon diode 80 is formed on the metal layer ofthe word line (WL) 91, and the underlayer 81 is formed on the diode 80.A nitride film such as TIN_(X) may be provided between the metal layerand the silicon diode to prevent atomic diffusion. The ferromagneticdouble tunnel junction element (TMR) 10 shown in FIG. 1 is formed on theunderlayer 81. That is, a first antiferromagnetic layer 11/a firstferromagnetic layer (pinned layer) 12/a first dielectric layer 13/asecond ferromagnetic layer (free layer) 14/a second dielectric layer15/a third ferromagnetic layers (pinned layers) 16 a and 16 b/a secondantiferromagnetic layer 17 are stacked on the underlayer 81. In theabove embodiment, the pinned layer is constituted by two layers 16 a and16 b. The metal layer of the bit line 92 is formed on the secondantiferromagnetic layer 17 of the TMR 10.

The MRAM having such a structure may have the similar effect to thatdescribed with respect to FIG. 7. That is, spins in the pinned layers 16b and 16 a is more stably pinned by the antiferromagnetic layer 17having a large area, and magnetic moments in the pinned layers 16 b and16 a are not rotated even by repeated writing. Thus, reduction in outputcan be effectively prevented. In addition, as the patterning process ofthe comparatively thick antiferromagnetic layer 17 is separated toanother process, it is possible to reduce process damage to the regionof the ferromagnetic tunnel junction, and to improve processingaccuracy.

For application of the MRAM, a three-layered film of a ferromagneticlayer/a nonmagnetic layer/a ferromagnetic layer may be used for a freelayer so that the ferromagnetic layers may be anti-ferromagneticallycoupled through the nonmagnetic layer. In such a structure, as themagnetic flux is confined in the three-layered film, influence of thestatic magnetic field to the pinned layer is prevented when the magneticmoments in the free layer is reversed by current magnetic field, andalso a leakage magnetic field from the recording layer can be loweredwhich makes it possible to reduce a switching magnetic field. Thus, itis possible to prevent the problem that the output is graduallydecreased owing to rotation of a part of the magnetic moments in themagnetization pinned layer by repeated writing. Preferably, aferromagnetic layer in the structure of the ferromagnetic layer/thenonmagnetic layer/the ferromagnetic layer, which is closer to the wordline for applying the current magnetic field, is made of a softerferromagnetic material or made thicker. When the two ferromagneticlayers forming the three-layered film are made to have a differentthickness from each other, it is preferable to make the thicknessdifference within the range of 0.5 to 5 nm.

Another MRAM according to the present invention will be described below.This MRAM comprises a ferromagnetic double tunnel junction elementhaving a first magnetization pinned layer with a pinned magnetizationdirection, a first dielectric layer, a magnetic recording layer with areversible magnetization direction, a second dielectric layer, and asecond magnetization pinned layer with a pinned magnetization direction.The magnetic recording layer comprises a three-layered film of amagnetic layer, a nonmagnetic layer and a magnetic layer, and the twomagnetic layers constituting the three-layered film areantiferromagnetically coupled. Since the two magnetic layers areantiferromagnetically coupled and the magnetic flux is confined in themagnetic recording layer, it may be possible to reduce the switchingmagnetic field and the current density flowing in a wire. Themagnetization directions in the regions of the two magnetization pinnedlayers in contact with the dielectric layers are substantiallyanti-parallel to each other. Thus, it may be possible to select eitheran up-spin current and a down-spin current to be supplied to themagnetic recording layer by choosing a pinned layer for flowing acurrent to the magnetic recording layer from the two magnetizationpinned layers. Therefore, the magnetization of the magnetic recordinglayer may be easily reversed by changing a direction for supplying thespin current, so that the current flowing in the TMR element may bereduced. Thus, the MRAM has a suitable structure to supply the spincurrent and the current magnetic field to the magnetic recording layerto control the current density flowing in the wire and the TMR element.

The antiferromagnetically coupled magnetic recording layer forming theabove ferromagnetic double tunnel junction element may be easily formedby alternately stacking ferromagnetic layers and nonmagnetic metallayers. Since the thinner the antiferromagnetically coupled magneticrecording layer is the easier fine processing may be possible, it ispreferable for the magnetic recording layer to be made of athree-layered film of a ferromagnetic layer/a nonmagnetic metal layer/aferromagnetic layer. Moreover, a three-layered film of a ferromagneticlayer/a soft magnetic layer/a ferromagnetic layer may be used as theferromagnetic layer. In particular, when a three-layered film in which asoft magnetic layer such as a Ni—Fe alloy is inserted between twoCo_(x)Fe_(1−x) layers (where 0.5≦×<1.0) is used for the ferromagneticlayer, switching magnetic field may be remarkably made low. The reasonis that the Ni—Fe alloy layer is fcc (111) oriented, and then theCo_(x)Fe_(1−x) layer on this layer also is fcc (111) oriented, so thatthe switching magnetic field of the Co_(x)Fe_(1−x) layer itself isreduced and also total value of magnetization of the ferromagnetic layeris reduced.

Therefore, examples of the antiferromagnetically coupled magneticrecording layer are: (a) a ferromagnetic layer/a nonmagnetic layer/aferromagnetic layer, (b) (a ferromagnetic layer/a soft magnetic layer/aferromagnetic layer)/a nonmagnetic layer/a ferromagnetic layer, (c) (aferromagnetic layer/a soft magnetic layer/a ferromagnetic layer)/anonmagnetic layer/(a ferromagnetic layer/a soft magnetic layer/aferromagnetic layer). In this case, strength of antiferromagneticcoupling is preferably as high as 0.01 erg/cm² or more. Themagnetization pinned layers may be antiferromagnetically coupled byforming a stacked structure similar to that of the magnetic recordinglayer.

Examples of a ferromagnetic double tunnel junction element used for theMRAM will be described below, referring to FIGS. 10 to 12.

A ferromagnetic double tunnel junction element of FIG. 10 has a stackedstructure of an underlayer 101/a first antiferromagnetic layer 102/afirst magnetization pinned layer 103/a first dielectric layer 104/amagnetic recording layer 105 comprising a three-layered film of aferromagnetic layer 105 a, a nonmagnetic layer 105 b and a ferromagneticlayer 105 c/a second dielectric layer 106/a second magnetization pinnedlayer 107/a second antiferromagnetic layer 108/a protective layer 109.

The ferromagnetic layer 105 a and the ferromagnetic layer 105 c of themagnetic recording layer 105 are antiferromagnetically coupled. Themagnetization directions of the first magnetization pinned layer 103 incontact with the first dielectric layer 104, and the secondmagnetization pinned layer 107 in contact with the second dielectriclayer 106 are anti-parallel to each other.

A ferromagnetic double tunnel junction element of FIG. 11 has a stackedstructure of an underlayer 111/a first antiferromagnetic layer 112/afirst magnetization pinned layer 113/a first dielectric layer 114/amagnetic recording layer 115 comprising a three-layered film of aferromagnetic layer 115 a, a nonmagnetic layer 115 b and a ferromagneticlayer 115 c/a second dielectric layer 116/a second magnetization pinnedlayer 117 comprising a three-layered film of a ferromagnetic layer 117a, a nonmagnetic layer 117 b and a ferromagnetic layer 117 c/a secondantiferromagnetic layer 118/a protective layer 119.

The ferromagnetic layer 115 a and the ferromagnetic layer 115 c of themagnetic recording layer 115 are antiferromagnetically coupled. Theferromagnetic layer 117 a and the ferromagnetic layer 117 c of thesecond magnetization pinned layer 117 are anti-ferromagneticallycoupled. The magnetization directions of the first magnetization pinnedlayer 113 in contact with the first dielectric layer 114, and theferromagnetic layer 117 a forming the second magnetization pinned layer117 in contact with the second dielectric layer 116 are anti-parallel toeach other.

In the above case, the length of the first magnetization pinned layer113 may be preferably formed longer than those of the secondmagnetization pinned layer 117 and the magnetic recording layer 115 soas to form a part of a wire. In such a structure, the magnetic flux isconfined in the second magnetization pinned layer 117 and the magneticrecording layer 115, and a leakage magnetic flux from the firstmagnetization pinned layer 113 formed longer has little influence, sothat influence of stray field on the magnetic recording layer isreduced.

A ferromagnetic double tunnel junction element of FIG. 12 has a stackedstructure of an underlayer 121/a first antiferromagnetic layer 122/afirst magnetization pinned layer 123 comprising a three-layered film ofa ferromagnetic layer 123 a, a nonmagnetic layer 123 b and aferromagnetic layer 123 c/a first dielectric layer 124/a magneticrecording layer 125 comprising a three-layered film of a ferromagneticlayer 125 a, a nonmagnetic layer 125 b and a ferromagnetic layer 125 c/asecond dielectric layer 126/a second magnetization pinned layer 127comprising a five-layered film of a ferromagnetic layer 127 a, anonmagnetic layer 127 b, a ferromagnetic layer 127 c, nonmagnetic layer127 d and a ferromagnetic layer 127 e/a second antiferromagnetic layer128/a protective layer 129.

The ferromagnetic layer 125 a and the ferromagnetic layer 125 c of themagnetic recording layer 125 are antiferromagnetically coupled. Theferromagnetic layer 123 a and the ferromagnetic layer 123 c of the firstmagnetization pinned layer 123 are antiferromagnetically coupled. Theferromagnetic layer 127 a, a ferromagnetic layer 127 c, and aferromagnetic layer 127 e of the second magnetization pinned layer 127are antiferromagnetically coupled. The magnetization directions of theferromagnetic layer 123 c forming the first magnetization pinned layer123 in contact with the first dielectric layer 114, and theferromagnetic layer 127 a forming the second magnetization pinned layer127 in contact with the second dielectric layer 126 are anti-parallel toeach other. Also in this case, the length of the first magnetizationpinned layer 123 may be preferably formed longer than those of thesecond magnetization pinned layer 117 and the magnetic recording layer115.

FIG. 13 is a sectional view of the MRAM using the ferromagnetic doubletunnel junction element of FIG. 11. A trench is formed in a SiO₂insulator on a Si substrate 151, and a word line 152 comprising metalembedded in the trench is formed. A SiO₂ insulator is formed on the wordline 152, on which metal wire 153 and a ferromagnetic double tunneljunction element (TMR element) are formed. As shown in FIG. 11, the TMRelement has a stacked structure of an underlayer 111/a firstantiferromagnetic layer 112/a first magnetization pinned layer 113/adielectric layer 114/a magnetic recording layer 115 comprising athree-layered film of a ferromagnetic layer 115 a, a nonmagnetic layer115 b and a ferromagnetic layer 115 c/a second dielectric layer 116/asecond magnetization pinned layer 117 comprising a three-layered film ofa ferromagnetic layer 117 a, a nonmagnetic layer 117 b and aferromagnetic layer 117 c/a second antiferromagnetic layer 118/aprotective layer 119. The TMR element is processed so as to have apredetermined junction area, and has a deposited interlayer insulationfilm at its periphery. A bit line 154 connected to the protective layer119 of the TMR element is formed on the interlayer insulation film.

In this MRAM, a current magnet field is applied (for example, to a hardaxis direction) to the magnetic recording layer 115 by flowing a currentin the word line 152, and also a down-spin current is injected from thebit line 154 through layers to the magnetic recording layer 115 or anup-spin current is injected from the metal wire 153 through layers tothe magnetic recording layer 115, thereby performing writing byreversing the magnetization direction of the magnetic recording layer115. Thus, the writing by the injection of the spin current and theapplication of the current magnetic field to the magnetic recordinglayer 115 may cause reduction in the spin current flowing in the TMRelement and in the current density flowing in the wire (word line).Therefore, even in an MRAM with a capacity of 1 Gb or more, it may bepossible to control the wire melting or the destruction of the tunnelbarrier layer (dielectric layer) of the TMR element and to improvereliability.

In the MRAM of FIG. 13, the current flowing in the bit line 154functions to apply a current magnetic field to the magnetic recordinglayer 115 in a different direction (for example, to an easy axisdirection) from that of the word line 152. In order to increase thecurrent magnetic field in this direction, to improve thecontrollability, and to reduce the spin current injected into themagnetic recording layer 115, the second word line 156 may be providedon the bit line 154 so as to extend in parallel with the bit line 154with intervening the insulator layer 155 therebetween, as shown in FIG.14. In the MRAM of FIG. 14, the reversal of the magnetization of themagnetic recording layer 115 may be repeated by a lower current, usingthe change in the direction of the current flowing in the TMR elementand in the second word line 156 together.

FIG. 15 is a sectional view of another magnetoresistive elementaccording to the present invention. The magnetoresistive element shownin FIG. 15 comprises a ferromagnetic double tunnel junction elementhaving a stacked structure of a first antiferromagnetic layer 161, afirst ferromagnetic layer 162, a first tunnel insulator 163, a secondferromagnetic layer 164, a first nonmagnetic layer 165, a thirdferromagnetic layer 166, a second nonmagnetic layer 167, a fourthferromagnetic layer 168, a second tunnel insulator 169, a fifthferromagnetic layer 170, and a second antiferromagnetic layer 171.

A magnetic recording layer 172 comprises the second ferromagnetic layer164, the first nonmagnetic layer 165, the third ferromagnetic layer 166,the second nonmagnetic layer 167 and the fourth ferromagnetic layer 168,sandwiched between the first tunnel insulator 163 and the second tunnelinsulator 169. The second and third ferromagnetic layers 164 and 166 areantiferromagnetically coupled through the first nonmagnetic layer 165,and their magnetization directions are kept anti-parallel to each other.Similarly, the third and fourth ferromagnetic layers 166 and 168 areantiferromagnetically coupled through the second nonmagnetic layer 167,and their magnetization directions are kept anti-parallel to each other.

The first ferromagnetic layer 162 is exchange-coupled with the firstantiferromagnetic layer 161, and has the pinned magnetization in thedirection of the arrows shown in the drawing. Similarly, the fifthferromagnetic layer 170 is exchange-coupled with the secondantiferromagnetic layer 171, and has the pinned magnetization in thesame magnetization direction as that of the first ferromagnetic layer162.

In the magnetoresistive element, the magnetization rotation is performedin the direction of the external magnetic field, with keeping theantiferromagnetic coupling among the second to fourth ferromagneticlayer 164, 166, 168, when an external magnetic field is applied in apredetermined direction. On the other hand, the first ferromagneticlayer 162 and the fifth ferromagnetic layer 170 are pinned byexchange-coupling with the first and second antiferromagnetic layer 161,171, so that they do not cause magnetization rotation in the externalmagnetic field allowing the magnetization rotation of the second tofourth ferromagnetic layer 164, 166, 168. Thus, logic “1” or logic “0”may be recorded on the second to fourth ferromagnetic layers 164, 166,168.

At this time, there is no increased diamagnetic field in a scaled-downelement, since the magnetic flux is confined between the second andthird ferromagnetic layers 164 and 166 antiferromagnetically coupledthrough the first nonmagnetic layer 165, and the magnetic flux isconfined between the third and fourth ferromagnetic layers 166 and 168antiferromagnetically coupled through the second nonmagnetic layer 167.Therefore, the reversal magnetic field Hsw required for themagnetization reversal, hardly depending on the size of the memorycells, is determined by the magnetic coercive force Hc of the second tofourth ferromagnetic layers 164, 166 and 168. That is, there may be highenergy conservation effect, since lower Hc may cause lower Hsw. Assumingthat the uniaxial anisotropy is Ku, and the magnetization intensity isM, the magnetic coercive force Hc may be ideally given as Hc=2Ku/M.Thus, use of a material with the low uniaxial anisotropy may realize theobject. Moreover, there may be obtained an advantage that the recordingbits are stable to the disturbing magnetic field, since the magneticflux is confined in the antiferromagnetically coupled second to fourthferromagnetic layer 164, 166 and 168.

In the magnetoresistive element of FIG. 15, since three ferromagneticlayers are included in the magnetic recording layer 172, the second andfourth ferromagnetic layers 164 and 168 of the magnetic recording layer172 have the same magnetization direction. In this case, the firstferromagnetic layer (magnetization pinned layer) 162 opposing to thesecond ferromagnetic layer 164 through the first tunnel insulator 163,and the fifth ferromagnetic layer (magnetization pinned layer) 170opposing to the fourth ferromagnetic layer 168 through the second tunnelinsulator 169, also, have the same magnetization direction. Thus, theremay be more options for selection of the antiferromagnetic materials,since it suffices to merely use the same material as the first andsecond antiferromagnetic layers 161 and 171 and to make themagnetization directions of the first ferromagnetic layer 162 and thatof the fifth ferromagnetic layer 170 to be identical.

It may be preferable that the magnetization value M3 of the thirdferromagnetic layer 166 is equal to the total magnetization value M(2+4)of the magnetization value M2 of the second ferromagnetic layer 164 andthe magnetization value M4 of the fourth ferromagnetic layer 168 inorder to effectively confine the magnetic flux in the second to fourthferromagnetic layers 164, 166 and 168. However, since magnetizationrotation of the recording layer becomes difficult when M3 is equal toM(2+4), it may be preferable that the above magnetization values areslightly different from each other.

For example, when the second to fourth ferromagnetic layers are made ofthe same material, the thickness T3 of the third ferromagnetic layer 166is made to be different from the total thickness T(2+4) of the secondand fourth ferromagnetic layers 164 and 168. In this case, it may bepreferable that the absolute value of the difference between T3 andT(2+4) is within a range from 0.5 nm to 5 nm.

It may be possible that the value of M3 is different from that of M(2+4)by using different materials for the second to fourth ferromagneticlayers 164, 166 and 168.

Moreover, it may be also possible that the value of M3 is different fromthat of M(2+4) by providing other ferromagnetic layer in contact withthe second to fourth ferromagnetic layer 164, 166 and 168 which areantiferromagnetically coupled. A magnetoresistive element of FIG. 16 hasa structure in which the ferromagnetic layer 168 b is provided incontact with the fourth ferromagnetic layer 168 among the second tofourth ferromagnetic layers 164, 166 and 168 which areantiferromagnetically coupled through the first and second nonmagneticlayers 164 and 167. In this case, if a soft magnetic material such aspermalloy, Fe, Co—Fe alloy and Co—Fe—Ni alloy is used as ferromagneticlayer 168 b, it may be preferably possible to perform the magnetizationrotation at a low magnetic field.

In the present invention, a magnetic layered film in which the twoferromagnetic layers 162 a and 162c are antiferromagnetically coupledthrough the non-magnetic layer 162 b may be used as the firstferromagnetic layer (magnetization pinned layer) 162, and a magneticlayered film in which the two ferromagnetic layers 170 a and 170 c areantiferromagnetically coupled through the non-magnetic layer 170 b maybe used as the fifth ferromagnetic layer (magnetization pinned layer)170. In such a structure, the magnetizations of the first and fifthferromagnetic layers 162 and 170 are more stably and firmly pinned. Inaddition, since a leakage magnetic field from the first and fifthferromagnetic layers 162 and 170 becomes low, there may be controlledmagnetic effects on the magnetic recording layer 172, so that recordingstability is increased.

When memory cells each having the above magnetoresistive element and atransistor are arrayed, the MRAM shown in FIG. 6 may be formed. Whenmemory cells each having the above magnetoresistive element and a diodeare arrayed, the MRAM shown in FIG. 8 may be formed.

Half metal such as NiMnSb and Co₂MnGe may be used for the material ofthe second to fourth ferromagnetic layers 164, 166 and 168, other thanCo, Fe, Co—Fe alloy, Co—Ni alloy, Co—Fe—Ni alloy, and the like. A highermagnetoresistive effect may be obtained by the use of the half metal,since the half metal has an energy gap in a half of the spin bands, sothat a higher reproduction output may be obtained.

Moreover, it may be preferable that the second to fourth ferromagneticlayers 164, 166 and 168 have weak uniaxial anisotropy in an in-planedirection. The uniaxial anisotropy which is too strong causes highmagnetic coercive force of each ferromagnetic layer to cause unfavorableswitching magnetic field. The intensity of the uniaxial anisotropy maybe 10⁶ erg/cm³ or less, preferably, 10⁵ erg/cm³ or less. The thicknessof each ferromagnetic layer may be 1 to 10 nm.

Various kinds of metal such as Cu, Au, Ag, Cr, Ru, Ir, Al and theiralloys may be used as materials for the first and second nonmagneticlayers 165 and 167 existing between the second to fourth ferromagneticlayers 164, 166 and 168, and causing antiferromagnetic coupling. Inparticular, Cu, Ru, and Ir may be preferable, since strongantiferromagnetic coupling may be obtained even with a thin thickness.The preferable range of the thickness of the nonmagnetic layers may be0.5 to 2 nm.

As mentioned above, Al₂O₃, NiO, silicon oxide, MgO, and the like may beused as materials for the tunnel insulator. The preferable range of thethickness of the tunnel insulator may be 0.5 to 3 nm. As mentionedabove, FeMn, IrMn, PtMn and the like may be used for theantiferromagnetic layers.

Then, a magnetoresistive head using the magnetoresistive element of thepresent invention will be described.

FIG. 18 is a perspective view of a magnetoresistive head assemblyprovided with a magnetoresistive head having a ferromagnetic doubletunnel junction element according to the present invention. An actuatorarm 201, being provided with a hole to fix it to a fixed axis in themagnetic disk apparatus, comprises a bobbin part holding a driving coil(not shown). A suspension 202 is fixed to one end of the actuator arm201. A head slider 203 provided with the magnetoresistive head havingferromagnetic double tunnel junction element in each form mentionedabove is installed at the tip of the suspension 202. Moreover, a leadwire 204 for reading and writing of signals is wired to the suspension202; one end of the lead wire 204 is connected to each electrode of themagnetoresistive head installed in the head slider 203; and the otherend of the lead wire 204 is connected to an electrode pad 205.

FIG. 19 is a perspective view of the internal structure of a magneticdisk apparatus provided with the magnetic head assembly shown in FIG.18.

A magnetic disk 211 is fixed to a spindle 212, and rotated by a motor(not shown) in response to control signals from a driving control part(not shown). The actuator arm 201 of FIG. 18 is fixed to a fixed axis213, and supports the suspension 202 and the head slider 203 at the tipof the suspension. When the magnetic disk 211 is rotated, theair-bearing surface of the had slider 203 opposing to the disk is keptin a glided state from the surface of the disk 211 by a predeterminedflying height to perform recording and reproducing of information. Avoice coil motor 214, a kind of a linear motor, is installed at theproximal end of the actuator arm 201. The voice coil motor 214 isconstituted by a driving coil (not shown) wound up around the bobbinpart of the actuator arm 201, and a magnetic circuit having a permanentmagnet arranged opposing to and surrounding the coil and a yoke. Theactuator arm 201 is supported by ball bearings (not shown) provided attwo positions of the upper and lower ends of the fixed axis 213, and canperform sliding motion by the action of the voice coil motor 214.

The first, second and fourth ferromagnetic double tunnel junctionelements (FIGS. 1, 2 and 4) may be preferably used, and the firstferromagnetic double tunnel junction element may be more preferably usedfor application of the magnetoresistive head. Moreover, the spins of theadjoining pinned layer and free layers are preferably perpendicular toeach other by deposition or heat treatment in the magnetic field for useof the magnetoresistive head. A linear response may be obtained for theleakage magnetic field from the magnetic disk with the above structureto have applications to any type of head structures.

EMBODIMENTS

The embodiments of the present invention will be described hereinafter.

Embodiment 1

An embodiment, where two kinds of ferromagnetic double tunnel junctionelements (sample A, and B) with the structure shown in FIG. 1 wereformed on a Si/SiO₂ substrate or SiO₂ substrate, will be describedbelow.

The sample A has a structure sequentially stacked with a TaN underlayer,a first antiferromagnetic layer of a two-layered film of Fe—Mn/Ni—Mn, afirst ferromagnetic layer of CoFe, a first dielectric layer of Al₂O₃, asecond ferromagnetic layer of Co₉Fe, a second dielectric layer of Al₂O₃,a third ferromagnetic layer of CoFe, a second antiferromagnetic layer ofa two-layered film of Ni—Fe/Fe—Mn, and a protective layer of Ta.

The sample B has a structure sequentially stacked with a TaN underlayer,a first antiferromagnetic layer of Ir—Mn, a first ferromagnetic layer ofCo—Fe, a first dielectric layer of Al₂O₃, a second ferromagnetic layerof a three-layered film of CoFe/Ni—Fe/CoFe, a second dielectric layer ofAl₂O₃, a third ferromagnetic layer of CoFe, a second antiferromagneticlayer of Ir—Mn, and a protective layer of Ta.

The sample A was made as follows. The substrate was put into asputtering apparatus. After setting the initial pressure at 1×10⁻⁷ Torr,Ar was introduced into the apparatus and the pressure was set at apredetermined value. Then, layers of Ta (5 nm)/Fe₅₄Mn₄₆ (20 nm)/Ni₈Fe₂(5 nm)/CoFe (3 nm)/Al₂O₃ (1.7 nm)/Co₉Fe (3 nm)/Al₂O₃ (2 nm)/CoFe (3nm)/Ni₈Fe₂ (5 nm)/Fe₅₄Mn₄₆ (20 nm)/Ta (5 nm) were sequentially stackedon the substrate. Here, the Al₂O₃ layer was formed by depositing Alusing an Al target in pure Ar gas, by introducing oxygen into theapparatus without breaking the vacuume, and then by exposing it to theplasma oxygen.

After deposition of the above stacked film, a first resist patterndefining a lower wire shape with a width of 100 μm was formed on theuppermost Ta protective layer by photolithography, and the above filmwas processed by ion milling.

Next, after removal of the first resist pattern, a second resist patterndefining a junction dimensions was formed on the uppermost Ta protectivelayer by photolithography, and the layers ofCo₉Fe/Al₂O₃/CoFe/Ni—Fe/Fe—Mn/Ta above the first Al₂O₃ layer wereprocessed by ion milling. The Al₂O₃ layer with a thickness of 300 nm wasdeposited by electron beam evaporation, while leaving the second resistpattern, and then the second resist pattern and the Al₂O₃ layer on theabove pattern were lifted off, thereby an interlayer insulation film wasformed in regions except the junction region.

Then, after forming the third resist pattern covering regions except theregion of the electrode wire, the surface was reverse-spattered andcleaned. After Al was deposited allover the surface, the third resistpattern and the Al on the pattern were lifted off, thereby the Alelectrode wire was formed. Then, after introduction into a heat-treatingfurnace in the magnetic field, the uniaxial anisotropy was introduced tothe pinned layer.

The sample B was made as follows. The substrate was put into asputtering apparatus. After setting the initial pressure at 1×10⁻⁷ Torr,Ar was introduced into the apparatus and the pressure was set at apredetermined value. Then, layers of Ta (5 nm)/Ir₂₂Mn₇₈ (20 nm)/CoFe (3nm)/Al₂O₃ (1.5 nm)/CoFe (1 nm)/Ni₈Fe₂ (t nm, t=1, 2, or 3 nm)/CoFe (1nm)/Al₂O₃ (1.8 nm)/CoFe (3 nm)/Ir₂₂Mn₇₈ (20 nm)/Ta (5 nm) weresequentially stacked on the substrate. Here, the Al₂O₃ layer was formedin a similar manner to the above method.

After deposition of the above stacked film, a first resist patterndefining a lower wire shape with a width of 100 μm was formed on theuppermost Ta protective layer by photolithography, and the above filmwas processed by ion milling. Next, after removal of the first resistpattern, a second resist pattern defining a junction dimensions wasformed on the uppermost Ta protective layer by photolithography, and thelayers of CoFe/Ni₈Fe₂/CoFe/Al₂O₃/CoFe/Ir₂₂Mn₇₈/Ta above the first Al₂O₃layer were processed by ion milling. Then, in a similar manner to theabove, the formation of the Al₂O₃ interlayer insulation film, and thatof the Al electrode wire, and the introduction of the uniaxialanisotropy to the pinned layer were performed.

For comparison, samples C and D described in the following were made.

The sample C is a ferromagnetic single tunnel junction element, and hasa stacked structure of Ta/Ir—Mn/CoFe/Al²O₃/CoFe/Ni—Fe/Ta.

The sample D is a ferromagnetic double tunnel junction element withoutan antiferromagnetic layer, and has a stacked structure of Ta (5nm)/CoPt (20 nm)/Al₂O₃ (1.5 nm)/CoFe (1 nm)/Ni₈Fe₂ (3 nm)/CoFe (1nm)/Al₂O₃ (1.8 nm)/CoPt (20 nm)/Ta (5 nm).

The magnetoresistive curves of the samples A and B are shown in FIG. 20.For the sample A, 27% of an MR change was obtained by a low magneticfield of 25 Oe. For the sample B, it is understood that the reversalmagnetic field may be controlled by changing the thickness ratio betweenthe Ni₈Fe₂ and CoFe layers in the free layer (magnetic recording layer).That is, when the thickness of the Ni₈Fe₂ layer is 1 nm, 2 nm and 3 nm,the resistance is largely changed by a low magnetic field of 16 Oe, 36Oe, and 52 Oe, respectively, to obtain a high MR change of 26% or more.

FIG. 21 shows applied voltage dependency of the MR change for thesamples A, B and C. Here, the MR change normalized by the value at 0V isshown in the drawing. The drawing exhibits that the samples A and B havea higher voltage of V_(½) at which the MR change is reduced to half, anda lower reduction in the MR change with increased voltage, compared tothe sample C.

Next, the samples A, B and D were put in a solenoid coil, and fatiguetests of the magnetization pinned layer in a magnetically recorded statewere conducted in a pulse magnetic field of 70 Oe. FIG. 22 shows therelationships between the reversal cycles and the output voltage of thepulse magnetic field for the sample A, B and D. In the drawing, theoutput voltage is normalized by an initial output voltage value. Asclearly shown in the drawing, the output voltage is remarkably reducedwith increase in the reversal cycles of the pulse magnetic field, in thecase of the sample D. On the other hand, there is found no fatigue inthe magnetization pinned layer in a magnetically recorded state in thecase of the samples A and B.

It is evident from the above that the ferromagnetic double tunneljunction element having a structure shown in FIG. 1 shows suitablecharacteristics for applications to a magnetic memory device and amagnetic head.

When SiO₂, AlN, MgO, LaAlO₃, or CaF₂ was used for the dielectric layer,the similar tendency to the above was found.

Embodiment 2

An embodiment, where two kinds of ferromagnetic double tunnel junctionelements (sample A2, and B2) with the structure shown in FIG. 2 wereformed on a Si/SiO₂ substrate or SiO₂ substrate, will be describedbelow.

The sample A2 has a structure sequentially stacked with a TaNunderlayer, a first ferromagnetic layer of a two-layered film ofNi—Fe/CoFe, a first dielectric layer of Al₂O₃, a second ferromagneticlayer of CoFe, an antiferromagnetic layer of Ir—Mn, a thirdferromagnetic layer of CoFe, a second dielectric layer of Al₂O₃, afourth ferromagnetic layer of a two-layered film of CoFe/Ni—Fe, and aprotective layer of Ta.

The sample B2 has a structure sequentially stacked with a TaNunderlayer, a first ferromagnetic layer of a three-layered film ofNi—Fe/Ru/CoFe, a first dielectric layer of Al₂O₃, a second ferromagneticlayer of a two-layered film of CoFe/Ni—Fe, a first antiferromagneticlayer of Fe—Mn, a third ferromagnetic layer of a two-stacked film ofNi—Fe/CoFe, a second dielectric layer of Al₂O₃, a fourth ferromagneticlayer of CoFe/Ru/Ni—Fe, and a protective layer of Ta.

The sample A2 was made as follows. The substrate was put into asputtering apparatus. After setting the initial pressure at 1×10⁻⁷ Torr,Ar was introduced into the apparatus and the pressure was set at apredetermined value. Then, layers of Ta (3 nm)/Ni₈₁Fe₁₉ (t nm, t=3, 5,or 8 nm)/CoFe (1 nm)/Al₂O₃ (1.2 nm)/CoFe (1 nm)/Ir₂₂Mn₇₈ (17 nm)/CoFe (1nm)/Al₂O₃ (1.6 nm)/CoFe (1 nm)/Ni₈₁Fe₁₉ (t nm, t=3, 5, or 8 nm)/Ta (5nm) were sequentially stacked on the substrate. Here, the Al₂O₃ layerwas formed by depositing Al using an Al target in pure Ar gas, byintroducing oxygen into the apparatus without breaking the vacuume, andthen by exposing it to the plasma oxygen.

After deposition of the above stacked film, a first resist patterndefining a lower wire shape with a width of 100 μm was formed on theuppermost Ta protective layer by photolithography, and the above filmwas processed by ion milling.

Next, after removal of the first resist pattern, a second resist patterndefining a junction dimensions was formed on the uppermost Ta protectivelayer by photolithography, and the layers ofCoFe/Ir—Mn/CoFe/Al₂O₃/CoFe/Ni—Fe/Ta above the first Al₂O₃ layer wereprocessed. The Al₂O₃ layer with a thickness of 300 nm was deposited byelectron beam evaporation, while leaving the second resist pattern, andthen the second resist pattern and the Al₂O₃ layer on the above patternwere lifted off, thereby an interlayer insulation film was formed inregions except the junction region.

Then, after forming the third resist pattern covering regions: exceptthe region of the electrode wire, the surface was reverse-spattered andcleaned. After Al was deposited allover the surface, the third resistpattern and the Al on the pattern were lifted off, thereby the Alelectrode wire was formed. Then, after introduction into a heat-treatingfurnace in the magnetic field, the uniaxial anisotropy was introduced tothe pinned layer.

The sample B2 was made as follows. The substrate was put into asputtering apparatus. After setting the initial pressure at 1×10⁻⁷ Torr,Ar was introduced into the apparatus and the pressure was set at apredetermined value. Then, layers of Ta (2 nm)/Ni₈₁Fe₁₉ (6 nm)/Ru (0.7nm)/Co₄Fe₆ (3 nm)/Al₂O₃ (1.5 nm)/CoFe (1 nm)/Ni₈₁Fe₁₉ (1 nm)/Fe₅₄Mn₄₆(20 nm)/Ni₈₁Fe₁₉ (1 nm)/CoFe (1 nm)/Al₂O₃ (1.7 nm)/Co₄Fe₆ (3 nm)/Ru (0.7nm)/Ni₈₁Fe₁₉ (6 nm)/Ta (5 nm) were sequentially stacked on thesubstrate. Here, the Al₂O₃ layer was formed in a similar manner to theabove method.

After deposition of the above stacked film, a first resist patterndefining a lower wire shape with a width of 100 μm was formed on theuppermost Ta protective layer by photolithography, and the above filmwas processed by ion milling. Next, after removal of the first resistpattern, a second resist pattern defining a junction dimensions wasformed on the uppermost Ta protective layer by photolithography, and thelayers of CoFe/N₈₁Fe₁₉/Fe₅₄Mn₄₆/Ni₈₁Fe₁₉/CoFe/Al₂O₃/Co₄Fe₆/Ru/N₈₁Fe₁₉/Taabove the first Al₂O₃ layer were processed by ion milling. Then, in asimilar manner to the above, the formation of the Al₂O₃ interlayerinsulation film, and that of the Al electrode wire, and the introductionof the uniaxial anisotropy to the pinned layer were performed.

For comparison, samples C2 and D2 described in the following were made.

The sample C2 is a ferromagnetic single tunnel junction element, and hasa stacked structure of Ta (3 nm)/Ni₈₁Fe₁₉ (5 nm)/CoFe (1 nm)/Al₂O₃ (1.2nm)/CoFe (1 nm)/Ir₂₂Mn₇₈ (17 nm)/CoFe (1 nm)/Ta (5 nm).

The sample D2 is a ferromagnetic double tunnel junction element withoutan antiferromagnetic layer, and has a stacked structure of Ta (3nm)/Ni₈₁Fe₁₉ (5 nm)/CoFe (1 nm)/Al₂O₃ (1.2 nm)/CoFe (1 nm)/Al₂O₃ (1.6nm)/CoFe (1 nm)/Ni₈₁Fe₁₉ (5 nm)/Ta (5 nm).

The magnetoresistive curves of the samples A2 and B2 are shown in FIG.23. For the sample A2, it is understood that the reversal magnetic fieldmay be controlled by changing the thickness ratio between the Ni₈Fe₂ andCoFe layers in the free layer (magnetic recording layer). That is, whenthe thickness of the Ni₈Fe₂ layer is 3 nm, 5 nm and 8 nm, the resistanceis largely changed by a low magnetic field of 15 Oe, 26 Oe and 38 Oe,respectively, to obtain a high MR change of 26% or more. In the case ofthe sample B2, the MR change of 26% is obtained by a low magnetic fieldof 39 Oe.

FIG. 24 shows applied voltage dependency of the MR change for thesamples A2, B2 and C2. Here, the MR change normalized by the value at 0Vis shown in the drawing. The drawing exhibits that the samples A2 and B2have a higher voltage of V_(½) at which the MR change is reduced tohalf, and a lower reduction in the MR change with increased voltage,compared to the sample C2.

Next, the samples A2, B2 and D2 were put in a solenoid coil, and fatiguetests of the magnetization pinned layer in a magnetically recorded statewere conducted in a pulse magnetic field of 70 Oe. FIG. 25 showsrelationships between the reversal cycles and the output voltage of thepulse magnetic field for the sample A2, B2 and D2. As clearly shown inthe drawing, the output voltage is remarkably reduced with increase inthe reversal cycles of the pulse magnetic field, in the case of thesample D2. On the other hand, there is found no fatigue in themagnetization pinned layer in a magnetically recorded state in the caseof the samples A2 and B2. Moreover, in comparison between the samples A2and B2, there is found less fatigue in the if sample B2 using anantiferromagnetically coupled three-layered structure ofCo₄Fe₆/Ru/Ni₈₁Fe₁₉ for the free layer.

It is evident from the above that the ferromagnetic double tunneljunction element having a structure shown in FIG. 2 shows suitablecharacteristics for applications to a magnetic memory device and amagnetic head.

When SiO₂, AlN, MgO, LaAlO₃, or CaF₂ was used for the dielectric layer,the similar tendency to the above was found.

Embodiment 3

An embodiment, where two kinds of ferromagnetic double tunnel junctionelements (sample A3, and B3) with the structure shown in FIG. 3 wereformed on a Si/SiO₂ substrate or SiO₂ substrate, will be describedbelow.

The sample A3 has a structure sequentially stacked with a TaNunderlayer, a first antiferromagnetic layer of Ir—Mn, a firstferromagnetic layer of Co—Fe, a first dielectric layer of Al₂O₃, asecond ferromagnetic layer of Co—Fe—Ni, a second antiferromagnetic layerof Fe—Mn, a third ferromagnetic layer of Co—Fe—Ni, a second dielectriclayer of Al₂O₃, a fourth ferromagnetic layer of Co—Fe, an thirdantiferromagnetic layer of Ir—Mn, and a protective layer of Ta.

The sample B3 has a structure sequentially stacked with a TaNunderlayer, a first antiferromagnetic layer of Ir—Mn, a firstferromagnetic layer of a three-layered film of Co—Fe/Ru/Co—Fe, a firstdielectric layer of Al₂O₃, a second ferromagnetic layer of a two-layeredfilm of CoFe/Ni—Fe, a second antiferromagnetic layer of Fe—Mn, a thirdferromagnetic layer of a two-layered film of Ni—Fe/CoFe, a seconddielectric layer of Al₂O₃, a fourth ferromagnetic layer of athree-layered film of Co—Fe/Ru/Coi—Fe, a third antiferromagnetic layerof Ir—Mn, and a protective layer of Ta.

The sample A3 was made as follows. The substrate was put into asputtering apparatus. After setting the initial pressure at 1×10⁻⁷ Torr,Ar was introduced into the apparatus and the pressure was set at apredetermined value. Then, layers of Ta (5 nm)/Ir₂₂Mn₇₈ (18 nm)/CoFe (2nm)/Al₂O₃ (1.7 nm)/Co₅Fe₁Ni₄ (2 nm)/Fe₁Mn₁ (17 nm)/Co₅Fe₁Ni₄ (2nm)/Al₂O₃ (2 nm)/CoFe (2 nm)/Ir₂₂Mn₇₈ (18 nm)/Ta (5 nm) weresequentially stacked on the substrate. Here, the Al₂O₃ layer was formedby depositing Al using an Al target in pure Ar gas, by introducingoxygen into the apparatus without breaking the vacuume, and then byexposing it to the plasma oxygen.

After deposition of the above stacked film, a first resist patterndefining a lower wire shape with a width of 100 μm was formed on theuppermost Ta protective layer by photolithography, and the above filmwas processed by ion milling.

Next, after removal of the first resist pattern, a second resist patterndefining a junction dimensions was formed on the uppermost Ta protectivelayer by photolithography, and the layers ofCo₅Fe₁Ni₄/Fe₁Mn₁/CoFeNi₄/Al₂O₃/CoFe/Ir₂₂Mn₇₈/Ta above the first Al₂O₃layer were processed by ion milling. The Al₂O₃ layer with a thickness of350 nm was deposited by electron beam evaporation, while leaving thesecond resist pattern, and then the second resist pattern and the Al₂O₃layer on the above pattern were lifted off, thereby an interlayerinsulation film was formed in regions except the junction region.

Then, after forming the third resist pattern covering regions except theregion of the electrode wire, the surface was reverse-spattered andcleaned. After Al was deposited allover the surface, the third resistpattern and the Al on the pattern were lifted off, thereby the Alelectrode wire was formed. Then, after introduction into a heat-treatingfurnace in the magnetic field, the uniaxial anisotropy was introduced tothe pinned layer.

The sample B3 was made as follows. The substrate was put into asputtering apparatus. After setting the initial pressure at 1×10⁻⁷ Torr,Ar was introduced into the apparatus and the pressure was set at apredetermined value. Then, layers of Ta (3 nm)/Ir—Mn (14 nm)/Co—Fe (1.5nm)/Ru (0.7 nm)/Co—Fe (1.5 nm)/Al₂O₃ (1.7 nm)/CoFe (1 nm)/Ni₈₁Fe₁₉ (2nm)/Fe₄₅Mn₅₅ (19 nm)/Ni₈₁Fe₁₉ (2 nm)/CoFe (1 nm)/Al₂O₃ (2.1 nm)/Co₉Fe (2nm)/Ru (0.8 nm)/Co₉Fe (2 nm)/Ir—Mn (14 nm)/Ta (5 nm) were sequentiallystacked on the substrate. Here, the Al₂O₃ layer was formed in a similarmanner to the above method.

After deposition of the above stacked film, a first resist patterndefining a lower wire shape with a width of 100 μm was formed on theuppermost Ta protective layer by photolithography, and the above filmwas processed by ion milling. Next, after removal of the first resistpattern, a second resist pattern defining a junction dimensions wasformed on the uppermost Ta protective layer by photolithography, and thelayers ofCoFe/Ni₈₁Fe₁₉/Fe₄₅Mn₅₅/Ni₈₁Fe₁₉/CoFe/Al₂O₃/Co₉Fe/Ru/Co₉Fe/Ir—Mn/Ta abovethe first Al₂O₃ layer were processed by ion milling. Then, in a similarmanner to the above, the formation of the Al₂O₃ interlayer insulationfilm, and that of the Al electrode wire, and the introduction of theuniaxial anisotropy to the pinned layer were performed.

For comparison, samples C3 and D3 described in the following were made.

The sample C3 is a ferromagnetic single tunnel junction element, and hasa stacked structure of Ta (3 nm)/Ir—Mn (14 nm)/Co—Fe (1.5 nm)/Ru (0.7nm)/Co—FE (1.5 nm)/Al₂O₃ (1.7 nm)/CoFe (1 nm)/Ni₈₁Fe₁₉ (2 nm)/Fe₄₅Mn₅₅(19 nm)/Ta (5 nm).

The sample D3 is a ferromagnetic double tunnel junction element withoutan antiferromagnetic layer, and has a stacked structure of Ta (5nm)/Co₈Pt₂ (15 nm)/CoFe (2 nm)/Al₂O₃ (1.7 nm)/CO₅Fe₁Ni₄ (2 nm)/Al₂O₃ (2nm)/CoFe (2 nm)/Co₈Pt₂ (15 nm)/Ta (5 nm).

The magnetoresistive curves of the samples A3 and B3 are shown in FIG.26. The sample A3 has 26% of an MR change by a low magnetic field of 57Oe, and the sample B3 has 27% of an MR change by a low magnetic field of63 Oe.

FIG. 27 shows applied voltage dependency of the MR change for thesamples A3, B3 and C3. Here, the MR change normalized by the value at 0Vis shown in the drawing. The drawing exhibits that the samples A3 and B3have a higher voltage of V_(½) at which the MR change is reduced tohalf, and a lower reduction in the MR change with increased voltage,compared to the sample C3.

Next, the samples A3, B3 and D3 were put in a solenoid coil, and fatiguetests of the magnetization pinned layer in a magnetically recorded statewere conducted in a pulse magnetic field of 75 Oe. FIG. 28 showsrelationships between the reversal cycles and the output voltage of thepulse magnetic field for the samples A3, B3 and D3. Here, The outputvoltage is normalized with the initial output voltage. As clearly shownin the drawing, the output voltage is remarkably reduced with increasein the reversal cycles of the pulse magnetic field, in the case of thesample D3. On the other hand, there is found no fatigue in themagnetization pinned layer in a magnetically recorded state in the caseof the samples A3 and B3. Moreover, in comparison between the sample A3and B3, there is found less fatigue in the sample B3 using anantiferromagnetically coupled three-layered structure of Co₉Fe/Ru/Co₉Fefor the free layer.

It is evident from the above that the ferromagnetic double tunneljunction element having a structure shown in FIG. 3 shows suitablecharacteristics for applications to a magnetic memory device and amagnetic head.

When SiO₂, AlN, MgO, LaAlO₃, or CaF₂ was used for the dielectric layer,the similar tendency to the above was found.

Embodiment 4

An embodiment, where two kinds of ferromagnetic double tunnel junctionelements (sample A4, and B4) with the structure shown in FIG. 4, or 5were formed on a Si/SiO₂ substrate or SiO₂ substrate, will be describedbelow.

The sample A4 has a structure sequentially stacked with a TaNunderlayer, a first antiferromagnetic layer of a two-layered film ofNi—Fe/Co—Fe, a first dielectric layer of Al₂O₃, a second ferromagneticlayer of Co—Fe, a first nonmagnetic layer of Ru, a third ferromagneticlayer of Co—Fe, a second nonmagnetic layer of Ru, a fourth ferromagneticlayer of Co—Fe, a second dielectric layer of Al₂O₃, a fifthferromagnetic layer of a two-layered film of Co—Fe/Ni—Fe, and aprotective layer of Ta.

The sample B4 has a structure sequentially stacked with a TaNunderlayer, a first ferromagnetic layer of a two-layered film ofNi—Fe/Co—Fe, a first dielectric layer of Al₂O₃, a second ferromagneticlayer of Co—Fe, a first nonmagnetic layer of Ru, a Co—Fe ferromagneticlayer/an Ir—Mn antiferromagnetic layer/a Co—Fe ferromagnetic layer, asecond nonmagnetic layer of Ru, a fourth ferromagnetic layer of Co—Fe, asecond dielectric layer of Al₂O₃, a fifth ferromagnetic layer of atwo-layered film of CoFe/Ni—Fe, and a protective layer of Ta.

The sample A4 was made as follows. The substrate was put into asputtering apparatus. After setting the initial pressure at 1×10⁻⁷ Torr,Ar was introduced into the apparatus and the pressure was set at apredetermined value. Then, layers of Ta (5 nm)/Ni₈₁Fe₁₉ (16 nm)/CO₄Fe₆(3 nm)/Al₂O₃ (1.7 nm)/CoFe (2 nm)/Ru (0.7 nm)/CoFe (2 nm)/Ru (0.7nm)/CoFe (2 nm)/Al₂O₃ (2 nm)/Co₄Fe₆ (3 nm)/Ni₈₁Fe₁₉ (16 nm)/Ta (5 nm)were sequentially stacked on the substrate. Here, the Al₂O₃ layer wasformed by depositing Al using an Al target in pure Ar gas, byintroducing oxygen into the apparatus without breaking the vacuume, andthen by exposing it to the plasma oxygen.

After deposition of the above stacked film, a first resist patterndefining a lower wire shape with a width of 100 μm was formed on theuppermost Ta protective layer by photolithography, and the above filmwas processed by ion milling.

Next, after removal of the first resist pattern, a second resist patterndefining a junction dimensions was formed on the uppermost Ta protectivelayer by photolithography, and the layers ofCoFe/Ru/CoFe/Ru/CoFe/Al2O₃/CO₄Fe₆/Ni₈₁Fe₁₉/Ta above the first Al₂O₃layer were processed by ion milling. The Al₂O₃ layer with a thickness of300 nm was deposited by electron beam evaporation, while leaving thesecond resist pattern, and then the second resist pattern and the Al₂O₃layer on the above pattern were lifted off, thereby an interlayerinsulation film was formed in regions except the junction region.

Then, after forming the third resist pattern covering regions except theregion of the electrode wire, the surface was reverse-spattered andcleaned. After Al was deposited allover the surface, the third resistpattern and the Al on the pattern were lifted off, thereby the Alelectrode wire was formed. Then, after introduction into a heat-treatingfurnace in the magnetic field, the uniaxial anisotropy was introduced tothe pinned layer.

The sample B4 was made as follows. The substrate was put into asputtering apparatus. After setting the initial pressure at 1×10⁻⁷ Torr,Ar was introduced into the apparatus and the pressure was set at apredetermined value. Then, layers of Ta (5 nm)/Ni₈₁Fe₁₉ (15 nm)/Co₉ Fe(2 nm)/Al₂O₃ (1.5 nm)/CoFe (1.5 nm)/Ru (0.7 nm)/CoFe (1.5 nm)/Ir—Mn (14nm)/CoFe (1.5 nm)/Ru (0.7 nm)/CoFe (1.5 nm)/Al₂O₃ (2 nm)/Co₉Fe (2nm)/Ni₈₁Fe₁₉ (15 nm)/Ta (5 nm) were sequentially stacked on thesubstrate. Here, the Al₂O₃ layer was formed in a similar manner to theabove method.

After deposition of the above stacked film, a first resist patterndefining a lower wire shape with a width of 100 μm was formed on theuppermost Ta protective layer by photolithography, and the above filmwas processed by ion milling. Next, after removal of the first resistpattern, a second resist pattern defining a junction dimensions wasformed on the uppermost Ta protective layer by photolithography, and thelayers of CoFe/Ru/CoFe/Ir—Mn/Cofe/Ru/CoFe/Al₂O₃/Co₉Fe/Ni₈₁Fe₁₉/Ta abovethe first Al₂O₃ layer were processed by ion milling. Then, in a similarmanner to the above, the formation of the Al₂O₃ interlayer insulationfilm, and that of the Al electrode wire, and the introduction of theuniaxial anisotropy to the pinned layer were performed.

For comparison, samples C4 and D4 described in the following were made.

The sample C4 is a ferromagnetic single tunnel junction element, and hasa stacked structure of Ta (5 nm)/Ni₈₁Fe₁₉ (16 nm)/Co₄Fe₆ (3 nm)/Al₂O₃(1.7 nm)/CoFe (2 nm)/Ru (0.7 nm)/CoFe (2 nm)/Ru (0.7 nm)/CoFe (2 nm)/Ta(5 nm).

The sample D4 is a ferromagnetic double tunnel junction element withoutan antiferromagnetic layer, and has a stacked structure of Ta (5nm)/Ni₈₁Fe₁₉ (16 nm)/Co₄Fe₆ (3 nm)/Al₂O₃ (1.7 nm)/CoFe (6 nm)/Al₂O₃ (2nm)/Co₄Fe₆ (3 nm)/Ni₈₁Fe₁₉ (16 nm)/Ta (5 nm).

The magnetoresistive curves of the samples A4 and B4 are shown in FIG.29. The sample A4 has 28% of an MR change by a low magnetic field of 33Oe, and the sample B4 has 26% of an MR change by a low magnetic field of18 oe.

FIG. 30 shows applied voltage dependency of the MR change for thesamples A4, B4 and C4. Here, the MR change normalized by the value at 0Vis shown in the drawing. The drawing exhibits that the samples A4 and B4have a higher voltage of V_(½) at which the MR change is reduced tohalf, and a lower reduction in the MR change with increased voltage,compared to the sample C4.

Next, the samples A4, B4 and D4 were put in a solenoid coil, and fatiguetests of the magnetization pinned layer in a magnetically recorded statewere conducted in a pulse magnetic field of 40 Oe. FIG. 31 showsrelationships between the reversal cycles and the output voltage of thepulse magnetic field for the samples A4, B4 and D4. Here, the outputvoltage is normalized with the initial output voltage. As clearly shownin the drawing, the output voltage is remarkably reduced with increasein the reversal cycles of the pulse magnetic field, in the case of thesample D4. On the other hand, there is found no fatigue in themagnetization pinned layer in a magnetically recorded state in the caseof the samples A4 and B4. Moreover, in comparison between the samples A4and B4, there is found less fatigue in the sample B4 using aseven-layered structure of CoFe/Ie/CoFe/Ir—Mn/CoFe/Ir/CoFe in which anantiferromagnetic layer is inserted into a magnetization pinned layers.

It is evident from the above that the ferromagnetic double tunneljunction element having a structure shown in FIG. 4 shows suitablecharacteristics for applications to a magnetic memory device and amagnetic head.

When SiO₂, AlN, MgO, LaAlO₃, or CaF₂ was used for the dielectric layer,the similar tendency to the above was found.

Embodiment 5

An embodiment, where a ferromagnetic double tunnel junction elements(samples A5 and B5 ) with the structure shown in FIG. 32 was made on aSi/SiO₂ substrate or SiO₂ substrate, considering the MRMA of FIG. 7 orFIG. 9, will be described below.

The sample A5 has a structure sequentially stacked with a TaNunderlayer, a first antiferromagnetic layer of Fe—Mn, a firstferromagnetic layer of a two-layered film of Ni—Fe/Co—Fe, a firstdielectric layer of Al₂O₃, a second ferromagnetic layer of Co₉—Fe, asecond dielectric layer of Al₂O₃, a third ferromagnetic layer of Co—Fe,a bit line (a third ferromagnetic layer of Ni—Fe, a secondantiferromagnetic layer of Fe—Mn, a metal layer of Al).

The sample B5 has a structure sequentially stacked with a TaNunderlayer, a first antiferromagnetic layer of Ir—Mn, a firstferromagnetic layer of Co—Fe, a first dielectric layer of Al₂O₃, asecond ferromagnetic layer of a three-layered film of Co—Fe/Ni—Fe/Co—Fe,a second dielectric layer of Al₂O₃, a third ferromagnetic layer ofCo—Fe, a bit line (a third ferromagnetic layer of Co, a secondantiferromagnetic layer of Ir—Mn, a metal layer of Al).

As shown in FIG. 32, both of the samples A5 and B5 have a larger area ofthe second antiferromagnetic layer than that of the junction area.

The sample A5 was made as follows. The substrate was put into asputtering apparatus. After setting the initial pressure at 1×10⁻⁷ Torr,Ar was introduced into the apparatus and the pressure was set at apredetermined value. Then, layers of Ta (5 nm)/Fe₅₄Mn₄₆ (18 nm)/Ni₈Fe₂(5 nm)/CoFe (2 nm)/Al₂O₃ (1.7 nm)/Co₉Fe (3 nm)/Al₂O₃ (2 nm)/CoFe (2nm)/Ta (5 nm) were sequentially stacked on the substrate. Here, theAl₂O₃ layer was formed by depositing Al using an Al target in pure Argas, by introducing oxygen into the apparatus without breaking thevacuume, and then by exposing it to the plasma oxygen.

After deposition of the above stacked film, a first resist patterndefining a lower wire shape with a width of 50 μm was formed on theuppermost Ta layer by photolithography, and the above film was processedby ion milling.

Next, after removal of the first resist pattern, a electron beam (EB)resist was applied to the uppermost Ta layer, and fine processing ofeach layer above the Al₂O₃ layer was performed, using an EB lithographyapparatus, to make ferromagnetic tunnel junction element with a junctionarea of 1×1 μm², 0.5×0.5 μm² or 0.15×0.15 μm². The Al₂O₃ layer with athickness of 300 nm was deposited by electron beam evaporation, whileleaving the EB resist pattern, and then the EB resist pattern and theAl₂O₃ layer on the above pattern were lifted off, thereby an interlayerinsulation film was formed in regions except the junction region.

Then, after forming the third resist pattern covering regions except theregion of the electrode wire, the surface was reverse-spattered andcleaned. Further, the Ta layer was removed. Then, Ni₈Fe₂ (5 nm)/Fe₅₄Mn₄₆(18 nm)/Al (5 nm) were sequentially stacked as the electrode wire of thebit line. The third resist pattern and the electrode wire on the patternwere lifted off. Then, after introduction into a heat-treating furnacein the magnetic field, the uniaxial anisotropy was introduced to thepinned layer.

The sample B5 was made as follows. The substrate was put into asputtering apparatus. After setting the initial pressure at 1×10⁻⁷ Torr,Ar was introduced into the apparatus and the pressure was set at apredetermined value. Then, layers of Ta (5 nm)/Ir₂₂Mn₇₈ (18 nm)/CoFe (3nm)/Al₂O₃ (1.5 nm)/CoFe (1 nm)/Ni₈Fe₂ (3 nm)/CoFe (1 nm)/Al₂O₃ (1.8nm)/CoFe (3 nm)/Ta (5 nm) were sequentially stacked on the substrate.Here, the Al₂O₃ layer was formed in a similar manner to the abovemethod.

After deposition of the above stacked film, a first resist patterndefining a lower wire shape with a width of 50 μm was formed on theuppermost Ta protective layer by photolithography, and the above filmwas processed by ion milling.

Next, after removal of the first resist pattern, an electron beam (EB)resist was applied to the uppermost Ta layer, and fine processing ofeach layer above the Al₂O₃ layer was performed, using an EB lithographyapparatus, to make ferromagnetic tunnel junction element with a junctionarea of 1×1 μm², 0.5×0.5 μm² or 0.15×0.15 μm². The Al₂O₃ layer with athickness of 300 nm was deposited by electron beam evaporation, whileleaving the second resist pattern, and the EB resist pattern and theAl₂O₃ layer on the above pattern were lifted off. Then, after formingthe third resist pattern covering regions except the region of theelectrode wire, the surface was reverse-spattered and cleaned. Further,the Ta layer was removed. Then, Co/Ir₂₂Mn₇₈ (18 nm)/Al (5 nm)/Al (5 nm)were sequentially stacked as the electrode wire of the bit line. Thethird resist pattern and the electrode wire on the pattern were liftedoff. Then, after introduction into a heat-treating furnace in themagnetic field, the uniaxial anisotropy was introduced to the pinnedlayer.

For comparison, samples C5, D5 and E5 described in the following weremade.

The sample C5 is a ferromagnetic single tunnel junction element, and hasa stacked structure of Ta (5 nm)/Ir₂₂Mn₇₈ (18 nm)/CoFe (3 nm)/Al₂O₃ (1.5nm)/CoFe (1 nm)/Ni₈Fe₂ (3 nm)/CoFe (1 nm)/Ta (5 nm).

The sample D5 has the similar stacked structure to that of the sampleB5, that is a structure sequentially stacked with Ta ((5 nm)/Ir₂₂Mn₇₈(18 nm)/CoFe (3 nm)/Al₂O₃ (1.5 nm)/CoFe (1 nm)/Ni₈Fe₂ (3 nm)/CoFe (1nm)/Al₂O₃ (1.8 nm)/CoFe (3 nm)/Ir₂₂Mn₇₈ (18 nm)/Ta (5 nm). However, thestructure is different from that of FIG. 32, that is, it is processed sothat the upper second antiferromagnetic layer of IrMn (and the Taprotective layer) has the same area as that of the junction area. Inaddition, the bit lines comprise only an Al layer.

The sample E5 is a ferromagnetic double tunnel junction element withoutan antiferromagnetic layer, and has a stacked structure of Ta (5nm)/CoFePt (13 nm)/Al₂O₃ (1.5 nm)/CoFe (1 nm)/Ni18FE2 (2 nm)/CoFe (1nm)/Al₂O₃ (1.8 nm)/CoFePt (13 nm)/Ta (5 nm).

The magnetoresistive curves of the samples A5 and B5 are shown in FIG.33. The sample A5 has 28% of an MR change by a low magnetic field of 29Oe, and the sample B5 has 27% of an MR change by a low magnetic field of39 Oe.

FIG. 34 shows applied voltage dependency of the MR change for thesamples A5, B5 and C5. Here, the MR change normalized by the value at 0Vis shown in the drawing. The drawing exhibits that the samples A5 and B5have a higher voltage of V_(½) at which the MR change is reduced tohalf, and a lower reduction in the MR change with increased voltage,compared to the sample C5.

Next, the samples A5, B5, D5 and E5 were put in a solenoid coil, andfatigue tests of the magnetization pinned layer in a magneticallyrecorded state were conducted in a pulse magnetic field of 70 Oe. FIG.35 shows relationships between the reversal cycles and the outputvoltage of the pulse magnetic field for the samples A5, B5, D5 and E5.Here, the output voltage is normalized with the initial output voltage.As clearly shown in the drawing, the output voltage is remarkablyreduced with increase in the reversal cycles of the pulse magneticfield, in the case of the sample E5. In the case of D5 shows a tendencyto cause much more fatigue as the lower junction area is reduced. It isassumed to be a reason that the smaller area causes deterioration of theupper magnetization pinned layer by process damage and the like. On theother hand, there is found no fatigue in the magnetization pinned layerin a magnetically recorded state in the case of the samples A5 and B5.Thus, it is evident that it is advantageous to have a structure with theupper antiferromagnetic layer as a part of bit lines as shown in FIG.32.

It is evident from the above that the ferromagnetic double tunneljunction element having a structure shown in FIG. 32 shows suitablecharacteristics for applications to, especially, a magnetic memorydevice.

When SiO₂, AlN, MgO, LaAlO₃, or CaF₂ was used for the dielectric layer,the similar tendency to the above was found.

Embodiment 6

A ferromagnetic double tunnel junction element having a basic structureshown in FIGS. 1 to 4 was made on an Si/SiO₂ substrate or an SiO₂substrate, in a similar manner to those of the Embodiments 1 to 4. Thestacked structures of the above elements are shown in Table 1. Here, anyone of Ta, Ti, Ti/Pt, Pt, Ti/Pd, Ta/Pt, Ta/Pd, and TiN_(X) was used forthe underlayer and the protective layer.

For the above samples, voltage of V_(½) at which the MR change isreduced to half, and a ratio of the output at 10000 reversal cycles andthe initial output of the free layer (magnetic recording layer) areshown in Table 1. Any samples have a higher MR change and a lowerreduction in the MR change with increased voltage, compared to those ofthe ferromagnetic single tunnel junction element. Moreover, there islittle reduction in the output voltage, and less fatigue with repeatedmagnetization reversal of the free layer (magnetic recording layer).

Thus, it is evident that the above elements show suitablecharacteristics for applications to a magnetoresistive head, a sensor,and a magnetic memory device.

Sample V_(1/2) (V) V₍₁₀₀₀₀₀₎/V_(initial)Ir₂₂Mn₇₈/Co₉Fe/SiO₂/Co₇Fe₃/SiO₂/Co₉Fe/Ir₂₂Mn₇₈ 0.71 0.98 (18 nm)(2nm)(1.8 nm)(2.4 nm)(1.9 nm)(3 nm)(20 nm)FeMn/Co₇Fe₂Ni/AlN/Co₇Fe₃/AlN/Co₇Fe₂Ni/FeMn 0.7 0.96 (17 nm)(3 nm)(1.9nm)(2.4 nm)(2.1 nm)(3 nm)(19 nm)PtMn/Ni₈Fe₂/Co₉Fe/Al₂O₃/Co₇Fe₃/Al₂O₃/Co₉Fe/Ni₈Fe₂/PtMn 0.79 0.99 (16nm)(3 nm)(2 nm)(1.4 nm)(2 nm)(1.9 nm)(1 nm)(2 nm)(20 nm)Ir₂₂Mn₇₈/Co₄Fe₆/MgO/CoFe/Ni₈Fe₂/CoFe/MgO/Co₄Fe₆/Ir₂₂Mn₇₈ 0.76 0.96 (17nm)(3 nm)(1.7 nm)(1 nm)(1 nm)(1 nm)(2.3 nm)(3 nm)(17 nm)Co₈₅Ni₁₅/SiO₂/Co₇Fe₂Ni/Ir₂₂Mn₇₈/Co₇Fe₂Ni/SiO₂/Co₈₅Ni₁₅ 0.77 0.97 (14nm)(2 nm)(1.5 nm)(18 nm)(1.5 nm)(2 nm)(17 nm)Ni₈Fe₂/CoFe/ALN/Co/FeNi₂/FeMn/FeNi₂/Co/AlN/Co/Fe 0.75 0.95 (1 nm)(7nm)(1.9 nm)(1 nm)(1 nm)(18 nm)(1.5 nm)(1 nm)(7 nm)(1 nm)Co₈₅Fe₁₅/Al₂O₃/Co₇Fe₂Ni/PtMn/Co₇Fe₂Ni/Al₂O₃/Co₈₅Fe₁₅ 0.81 0.91 (10nm)(1.7 nm)(2 nm)(18 nm)(2 nm)(2 nm)(14 nm)Co₈₀Pt₂₀/MgO/CoFe/Ru/CoFe/NiMn/Co₆Fe₃Ni/MgO/Co₈₀pt₂₀ 0.74 0.94 (12nm)(2.1 nm)(1.5 nm)(0.7 nm)(1 nm)(15 nm)(2 nm)(2.2 nm)(15 nm)Ir₂₂Mn₇₈/CoFeNi/SiO₂/FeCo₂Ni/FeMn/FeCo₂Ni/SiO₂/CoFeNi/Ir₂₂Mn₇₈ 0.71 0.91(19 nm)(3 nm)(2 nm)(1.6 nm)(15 nm)(1.6 nm)(2 nm)(2 nm)(19 nm)Ir₂₂Mn₇₈/Co₉Fe/Al₂O₃/FeCo/Ir₂₂Mn₇₈/FeCo/Al₂O₃/Co₉Fe/Ir₂₂Mn₇₈ 0.78 0.98(19 nm)(3 nm)(1.8 nm)(1.6 nm)(13 nm)(1.6 nm)(2 nm)(2 nm)(19 nm)Ir₂₂Mn₇₈/CoFe/AlN/FeCo₃Ni/Ir₂₀Mn₈₀/FeCo₃Ni/AlN/CoFe/Ir₂₂Mn₇₈ 0.78 0.98(19 nm)(2 nm)(2.2 nm)(1.5 nm)(17 nm)(1.5 nm)(2.2 nm)(2 nm)(19 nm)PtMn/CoFeNi/MgO/FeCo₂Ni₂/FeMn/FeCo₂Ni₂/MgO/CoFeNi/PtMn 0.81 0.91 (20m)(3 nm)(2.2 nm)(1.6 nm)(15 nm)(1.6 nm)(2.2 nm)(2 nm)(20 nm)CoFeNi/SiO₂/FeCo/Ru/FeCo/Ru/Co/SiO₂/CoFeNi 0.73 0.97 (15 nm)(2 nm)(1.5nm)(0.7 nm)(1.5 nm)(0.7 nm)(1.5 nm)(2 nm)(17 nm)CoFePt/AlN/Co/Ru/Co/Ru/Co/AlN/CoFePt 0.78 0.98 (15 nm)(2 nm)(1 nm)(0.7nm)(1 nm)(0.7 nm)(1 nm)(2 nm)(17 nm)CoFeNi/SiO₂/FeCo/Ru/FeCo/Ir₂₂Mn₇₈/CoFe/Ru/CoFe/SiO₂/CoFeNi 0.78 0.98 (14nm)(2 nm)(1.7 nm)(0.8 nm)(1.6 nm)(17 nm)(1.6 nm)(0.8 nm)(1.7 nm)(2.1nm)(14 nm) CoFe/AlN/FeCo/Ir/FeCo/PtMn/CoFe/Ir/CoFe/AlN/CoFe 0.81 0.91(15 nm)(1.4 nm)(1 nm)(0.9 nm)(1 nm)(17 nm)(1 nm)(0.9 nm)(1 nm)(2.1nm)(15 nm)

Note that, in the present invention, atomic diffusion and mixing betweenlayers may be caused. For example, under strong spattering, it isthought that the atomic diffusion may be caused between a NiFe alloylayer and a Co-based alloy layer, or between these layers and anonmagnetic layer or an antiferromagnetic layer. In addition, it isassumed that the similar atomic diffusion may be caused by heattreatment, depending on the temperature and time. If constituentmaterials for each layer show required magnetic characteristics in thepresent invention even if such atomic diffusion is caused and areincluded in the materials defined in the invention, they may be includedin the scope of the present invention.

Embodiment 7

An embodiment, where three kinds of ferromagnetic double tunnel junctionelements (sample T1, T2 and T3), having different thickness of the freelayer, with a structure shown in FIG. 1 were made on a Si/SiO₂ substrateor SiO₂ substrate, will be described below.

The sample T1 has a structure sequentially stacked with layers of a TaNunderlayer, a first antiferromagnetic layer of a two-layered film ofFe—Mn/Ni—Fe, a first ferromagnetic layer of CoFe, a first dielectriclayer of Al₂O₃, a second ferromagnetic layer of Co₉Fe, a seconddielectric layer of Al₂O₃, a third ferromagnetic layer of CoFe, a secondantiferromagnetic layer of a two-layered film of Ni—Fe/Fe—Mn, and a Taprotective layer, and the free layer that is the second ferromagneticlayer of Co₉Fe is 2.5 nm thick.

The sample T1 was made as follows. The substrate was put into asputtering apparatus. After setting the initial pressure at 1×10⁻⁷ Torr,Ar was introduced into the apparatus and the pressure was set at apredetermined value. Then, layers of Ta (5 nm)/Fe₅₄Mn₄₆ (20 nm)/Ni₈Fe₂(5 nm)/CoFe (3 nm)/Al₂O₃ (1.7 nm)/Co₉Fe (2.5 nm)/Al₂O₃ (2 nm)/CoFe (3nm)/Ni₈Fe₂ (5 nm)/Fe₅₄Mn₄₆ (20 nm)/Ta (5 nm) were sequentially stackedon the substrate. Here, the Al₂O₃ layer was formed by depositing Alusing an Al target in pure Ar gas, by introducing oxygen into theapparatus without breaking the vacuume, and then by exposing it to theplasma oxygen.

After deposition of the above stacked film, a resist pattern defining alower wire shape with a width of 100 μm was formed on the uppermost Taprotective layer by photolithography, and the above film was processedby ion milling.

Then, after removal of the resist pattern, a Ti hard mask defining ajunction dimensions was formed on the uppermost Ta protective layer byphotolithography and RIE (reactive ion etching), and the layers ofCo₉Fe/Al₂O₃/CoFe/Ni—Fe/Fe—Mn/Ta above the first Al₂O₃ layer wereprocessed by ion milling. The junction widthes were variously changed bythe above process. The EB lithography was used for fabricating elementswith a junction width 1 μm or less. After forming the resist pattern onthe junction region, and deposition of a SiO₂ layer with a thickness of300 nm by spattering or plasma CVD, the resist pattern and the SiO₂layer on the pattern were lifted off, thereby interlayer insulation filmwas formed on regions except the junction region.

Then, after forming a resist pattern covering regions except the regionof the electrode wire, the surface was reverse-spattered and cleaned.After Al was deposited allover the surface, the resist pattern and theAl on the pattern were lifted off, thereby the Al electrode wire wasformed. Then, after introduction into a heat-treating furnace in themagnetic field, the uniaxial anisotropy was introduced to the pinnedlayer.

The sample T2 has a free layer, the second ferromagnetic layer of Co₉Fe,of 7 nm thick, and it was made in a similar manner to that of the sample11.

The sample T3 has a free layer, the second ferromagnetic layer of Co₉Fe,of 17 nm thick, and it was made in a similar manner to that of thesample 11.

FIG. 36 shows relationships between junction width of the element andreversal magnetic field of the free layer for the samples T1 and T2.Here, the horizontal axis is a reciprocal (1/W) of the junction width W,in the drawing. AS shown in FIG. 36, any of the samples have the moreincreased reversal magnetic field according to the more reduced junctionwidth. That is, in the application of the MRAM, there may be the moreincreased power consumption for writing, according to the more reducedjunction width. However, in the case of the sample T1 having a thin freelayer, the inclination of the straight line is gentle, and the increaseof the reversal magnetic field according to the reduced junction widthmay be controlled. On the other hand, in the case of the samples T2 andT3 having a relatively thick free layer, the increase of the reversalmagnetic field according to the reduced junction width is remarkable,and in the application of the MRAM, the power consumption for writing islikely to be remarkably increased. Here, taking up elements with ajunction width of 0.25 μm (1/W=4) obtained by a current processingtechnology, the reversal magnetic fields will be compared. In the caseof the sample T1, the reversal magnetic field is lower than 100 Oe, andfurther fine processing may be realized. On the other hand, in the caseof the samples T2 and T3, the reversal magnetic field exceeds 100 Oe,and the further fine processing may be difficult, since the powerconsumption for writing is already high in the application of the MRAM.

FIG. 37 shows applied voltage dependency of the MR change for thesamples T1, T2 and T3. Here, the MR change normalized by the value at 0Vis shown in the drawing. In the case of the sample T1 having a thin freelayer, a bias voltage of V_(½), at which the MR change is reduced tohalf, exceeds 0.9V to control the bias voltage dependency. On the otherhand, in the case of the samples T2 and T3 having a thick free layer,the bias dependency is low compared to that of a ferromagnetic singletunnel junction element, but the V_(½) is less than 0,8V. That is, theyare clearly inferior to the sample T1.

It is evident from FIGS. 36 and 37 that the thinner free layer causesthe more controlled increase according to finer junction and improvementof the bias voltage dependency. When the thickness of the free layer is5 nm or less, the reversal magnetic field may be controlled to 100 Oe orless in the case of the element by 0.25 μm rule, and the bias dependencyof the MR change may be improved. However, when the thickness of a freelayer becomes less than 1 nm, the free layer is not made a continuousfilm, and likely to be a so-called granular structure in whichferromagnetic particles are dispersed in a dielectric layer. Thus, itmay be difficult to control the junction characteristics, and, dependingon the size of the fine particles, they may be in a superparamagneticstate at a room temperature to cause remarkable reduction in the MRchange. Therefore, the thickness of the free layer may be preferably 1to 5 nm.

Embodiment 8

An embodiment, where an MRAM with a structure shown in FIG. 14 was madeon a Si/SiO₂ substrate. SiO₂ was deposited on a Si substrate 151 byplasma CVD. A word line 152 was formed using a damascene process. Thatis, after application of a resist, a resist pattern was formed withphotolithography, trenches were processed on the SiO₂ by the RIE, Cu wasembedded into the trenches using the plating, and flattening wasperformed by CMP to form the word line 152. Then, a SiO₂ interlayerinsulation film with a thickness of 250 nm was formed on the word line152 by plasma CVD.

The sample was put into a sputtering apparatus. After setting theinitial pressure at 1×10⁻⁸ Torr, Ar was introduced into the apparatusand the pressure was set at a predetermined value. Then, layers of a TaNunderlayer/Cu (50 nm)/Ni₈₁Fe₁₉ (5 nm)/Ir₂₂Mn₇₈ (12 nm)/Co₅₀Fe₅₀ (3nm)/Al₂O₃ (1 nm)/Co₉₀Fe₁₀ (2 nm)/Ni₈₁Fe₁₉ (1 nm)/Co₉₀Fe₁₀ (2 nm)/Ru (0.9nm)/Co₉₀Fe₁₀ (2 nm)/Ni₈₁Fe₁₉ (1 nm)/Co₉₀Fe₁₀ (2 nm)/Al₂O₃ (1nm)/Co₈₀Fe₂₀ (3 nm)/Ru (0.9 nm)/Co₈₀Fe₂₀/Ir₂₂Mn₇₈ (12 nm)/Ni₈₁Fe₁₉ (5nm)/Au protection film were stacked on the SiO₂ interlayer insulationfilm. The Al₂O₃ layer was formed by depositing Al using an Al target inpure Ar gas, by introducing oxygen into the apparatus without breakingthe vacuume, and then by exposing it to the plasma oxygen.

After deposition of a Si₃N₄ layer on the above layered film andapplication of a resist, a resist pattern was formed by photolithographyto form a hard mask defining a metal wire 153 by RIE. Then, ion millingwas performed to process the stacked film. After that, the resistpattern was removed.

Next, the resist was applied, a resist pattern defining a junctiondimensions was formed by photolithography. Then, the films above thefirst Al₂O₃ layer were processed by ion milling, thereby the TMR elementwas formed. All the cell size of the TMR elements was set to 0.4×0.4μm². After that, the resist pattern was removed.

Next, after deposition of an SiO₂ interlayer insulation film by plasmaCVD, the flattening was performed by polishing it to a thickness of 250nm by CMP. Cu and an insulation film and Cu were stacked allover thesurface. A Si₃N₄ film was deposited on the stacked film. Afterapplication of the resist, a resist pattern was formed byphotolithography. After forming a hard mask by RIE, ion milling wasperformed to form a bit line 154, interlayer insulation layer 155 andthe second word line 156. Then, after introduction into a heat-treatingfurnace in the magnetic field, uniaxial anisotropy was introduced to themagnetic recording layer, and unidirectional anisotropy to themagnetization pinned layer.

Writing was performed on the obtained MRAM by the following threemethods.

(1) A method in which, while injecting the spin current of 1 mA into theTMR element, current pulses of 10 nsec is flowed in the word line 152and the second word line 156 to apply a current magnetic field in aneasy axis direction and hard axis direction of the magnetic recordinglayer 115.

(2) A method in which only injection of the spin current into the TMRelement is performed.

(3) A method in which current pulses of 10 nsec is flowed in the wordline 152 and the second word line 156 to apply a current magnetic fieldin an easy axis direction and hard axis direction of the magneticrecording layer 115.

The current pulse to apply current magnetic field in a hard axisdirection of the magnetic recording layer 115 was set to constantly be10 nsec and 3 mA.

The magnetization reversal of the magnetic recording layer 115 wasdecided by applying a direct current to the TMR cell after writing, andchecking whether there was a change in the output voltage.

In the method of (2) in which only injection of a spin current into theTMR element is performed, there was found no magnetization reversal evenwhen the current was increased to 10 mA. In the method of (3) in whichthe current magnetic field is applied in the direction of an easy axisand that of a hard axis of the magnetic recording layer 115, the currentfor applying the current magnetic field in the easy axis direction ofmagnetic recording layer 115 was required to be increased to 4.3 mA tocause the magnetization reversal.

On the other hand, according to the method of (1), when a current forapplying the current magnetic field in an easy axis direction of themagnetic recording layer 115 was increased while injecting a spincurrent of 1 mA, it was confirmed that the magnetization reversal of themagnetic recording layer 115 was attained at a current of 2.6 mA.Moreover, it was found that repeated magnetization reversal of themagnetic recording layer 115 could be attained at the above low current,by changing the direction of the current for applying the currentmagnetic field in an easy axis direction of the magnetic recording layer115 and that of the spin current flowing in the TMR element.

Thus, a suitable structure for injection of the spin current may berealized, and the current flowing in the wire for applying a currentmagnetic field and the current flowing in the TMR element may bereduced, if the structure of the MRAM and the writing method accordingto the present embodiments are used. Therefore, the melting of wire orthe destruction of the tunnel barrier layer may be controlled to improvethe reliability, even when the wire width and the size of TMR elementare more reduced with higher density of the MRAM.

Embodiment 9

An embodiment, where a magnetoresistive element with a structure shownin FIG. 16 was made, will be described. On a thermal oxidized Sisubstrate 151, an underlayer of Ta (10 nm)/NiFe (10 nm), a firstantiferromagnetic layer 161 of IrMn (50 nm), a fist ferromagnetic layer162 of Co₉Fe (1.5 nm), a first tunnel insulator 163 of Al₂O₃ (1.5 nm), asecond ferromagnetic layer 164 of Co₉Fe (1.5 nm), a first nonmagneticlayer 165 of Ru (0.8 nm), a third ferromagnetic layer 166 of Co₉Fe (1.5nm), a second nonmagnetic layer 167 of Ru (0.8 nm), a ferromagneticlayer 168 b of NiFe (2.0 nm), a fourth ferromagnetic layer 168 of Co₉Fe(1.5 nm), a second tunnel insulator 169 of Al₂O₃ (1.5 nm), a fifthferromagnetic layer 170 of Co₉Fe (1.5 nm), and a secondantiferromagnetic layer 171 of IrMn (50 nm) were sequentially stackedusing a magnetron spattering apparatus. In this element, the secondferromagnetic layer 164, the first nonmagnetic layer 165, the thirdferromagnetic layer 166, the second nonmagnetic layer 167, theferromagnetic layer 168 b and the fourth ferromagnetic layer 168constitute the magnetic recording layer 172. In the magnetic recordinglayer 172, the second and third ferromagnetic layers 164, 166 areantiferromagnetically coupled through the first nonmagnetic layer 165,and the third and fourth ferromagnetic layers 166 and 168 areantiferromagnetically coupled through the second nonmagnetic layer 167.The NiFe ferromagnetic layer 168 b is provided so that the magnetizationvalue M3 of the third ferromagnetic layer 166 and the totalmagnetization values M(2+4) of the second and fourth ferromagneticlayers 164 and 168 are made different from each other.

All the films were formed without breaking the vacuume. Al₂O₃constituting the first and second tunnel insulators 163 and 169 wasformed by plasma oxidation after spattering of Al metal. The underlayer,the first antiferromagnetic layer 161 and the first ferromagnetic layer162 were deposited through a mask with an opening having a lower wireshape with a width of 100 μm. Al to be converted to the first tunnelinsulator 163 was deposited through a mask with an opening having ashape of the junction. Each layer above the first tunnel insulator 163was deposited through a mask with an opening having a shape of the upperwire with a width of 100 μm extending in the direction perpendicular tothe lower wire. In the above processing, the above masks were exchangedin the vacuum chamber. Thus, the junction area was made 100×100 μm². Theuniaxial anisotropy was introduced in the film surface by applying themagnetic field of 100 Oe at deposition

It was observed from the measurements of the magnetic resistance for theabove magnetoresistive elements, using the four-terminal method, thatthere was 22% of an MR change under a low switching magnetic field ofabout 10 Oe, respectively.

Embodiment 10

Magnetoresistive elements with smaller junction area than that of theEmbodiment 9, and with the similar stacked structure to that of theEmbodiment 9 by fine processing using the photolithography were made.The area of the tunnel junction was made 5×5 μm², 1×1 μm², or 0.4×0.4μm².

It was observed from the measurements of the magnetic resistance for theabove magnetoresistive elements, using the four-terminal method, thatthere was an MR change under a low switching magnetic field of 12 Oe, 25Oe, and 35 Oe, respectively. There was no remarkable increase in theswitching magnetic field even under he small junction area as shownabove. The reason is supposed to be that, the generated diamagneticfield does not depend on the element size so much, as layered magneticfilms antiferromagnetically coupled are used for the magnetic recordinglayer.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A magnetic memory device comprising: a memorycell comprising a first magnetization pinned layer whose magnetizationdirection is pinned, a first dielectric layer, a magnetic recordinglayer whose magnetization direction is reversible, a second dielectriclayer, and a second magnetization pinned layer whose magnetizationdirection is pinned, the first magnetization pinned layer, the firstdielectric layer, the magnetic recording layer, the second dielectriclayer, and the second magnetization pinned layer being stacked in theorder recited, the magnetic recording layer comprising a three-layeredfilm of a magnetic layer, a nonmagnetic layer and a magnetic layer, thetwo magnetic layers constituting the three-layered film beinganti-ferromagnetically coupled, magnetization directions of the twomagnetization pinned layers in regions in contact with each dielectriclayer being substantially anti-parallel to each other, magnetizationdirections of the first magnetization pinned layer and the magneticlayer of the magnetic recording layer in regions in contact with thefirst dielectric layer being substantially parallel or anti-parallel toeach other when no current magnetic field is applied, and magnetizationdirections of the second magnetization pinned layer and the magneticrecording layer of the magnetic recording layer in regions in contactwith the second dielectric layer being substantially parallel oranti-parallel to each other when no current magnetic field is applied; abit line extending to a first direction; and a word line extending to asecond direction crossing the first direction.
 2. A method for writinginformation to the magnetic memory device according to claim 1,comprising steps of: supplying the magnetic recording layer with a spincurrent through the first or second magnetization pinned layer and thebit line; and flowing a current in the word line so as to apply acurrent magnetic field to the magnetic recording layer.
 3. The magneticmemory device according to claim 1, wherein the second magnetizationpinned layer comprises a three-layered film of a magnetic layer, anonmagnetic layer and a magnetic layer, the two magnetic layersconstituting the three-layered film being anti-ferromagneticallycoupled, and wherein a length of the first magnetization pinned layer isformed longer than that of the second magnetization pinned layer and themagnetic recording layer such that influence of a stray field from thefirst magnetization pinned layer on the magnetic recording layer isreduced.